To be honest, I've never seen Japanese ads like that, they tend to be less direct than that. Instead of "Buy X here!" they tend to be more like "X" in big text, and "1000 yen" or slogans in tiny text. Slogans occasionally appear in larger text, but they're always indirect, e.g. "enjoy our super-classy rocket engines" rather than "buy our high-quality rocket engines". On the bright side - you can make that text be too small to read ;D

Also, advertising just about everywhere, after people figured out how to do images, relies more on imagery than text. Use that to your advantage! It'll make your world look more interesting than text, and the ads will be understood by your players too.

But, if you want a very text-heavy world for some reason, here are a few ideas:
ここでXを買いまして - buy X here - like I said, I've never actually seen this used in any type of advertising because it's too direct, this kind of approach feels very American to me xP I have no idea how to translate the more general "shop here", I've never seen anything like that.
Xはここである - X is here / we have X, also Xは中にある X is inside/we have X (inside the shop). I've never seen either of these used, so if you use these, don't blame me if someone complains that they sound unnatural.
スペース・コーク。宇宙中の最高。 (supeesu-kooku. uchuujuu no saikou) Space Coke. Best in the universe/cosmos (lit. Universe-wide's best). 最高 is the most common term for "best, supreme", and it's literally "most high" - and what's higher than space?
ワルキューレと一緒に負けない - You won't lose with (the) Valkyrie(s). For the Valkyrie Supply shop.

Many Thanks! If you can't think of a good translation for the rest then don't worry about it. All the signs don't have to have the additional Japanese. These are all really good and should add the extra immersion that I'm looking for. 

Again, Thankyou very much! 

I had fun with these, even learned a few new words! I didn't do all of them, but I hope these help:

Surely Scrap: Two possibilities:
1. てっきりてつくず or てっきり鉄屑 (tekkiri tetsukuzu), but the hiragana spelling makes the alliteration/assonance more obvious. Literally means "Certainly Scrap-metal". Since this one's quite long, you may want to lay this one out so the two languages are stacked one above the other, not side by side.
2. きっと屑 (kitto kuzu). Simple alliteration and without specifying whether the scrap is metal or food or what, similar to the English name. This one has the same sense of doubt that "Surely Scrap" does - "surely" and "kitto" both denote certainty but are often used to express hope in an uncertain situation, e.g. "surely she'll live".

Black Knight Repair: Not a pun but a cultural reference, so here's a literal translation of the name: 黒騎士修理屋 (kurokishi shuriya, Black Knight Repair Shop). In the Japanese version of the film, the black knight was called 黒騎士 (kurokishi, literally "black knight"). You could also just call it 黒騎士 , with 修理屋 as a subtitle rather than as part of the title proper, this is fairly common with Japanese businesses. If you go the subtitle route, I recommend making the logo be the Black Knight's helmet and wrenches as "crossbones", to make a clear visual connection between "repair" and "Black Knight".

Valkyrie Supply: Literal translation: ワルキューレ支給, but I don't recommend this because in Japanese, 支給 ("supply") isn't used for stores as far as I know, it has strictly a "thing(s) supplied or rationed" sense. I'm not sure what to suggest that gives the same feel. I assume this is all about equipping your ship (rather than equipping personnel), so perhaps 設備 (equipment, facilities, things installed in a building) might be suitable. ワルキューレ(の)設備 (Walkyure('s) Setsubi) or something.

Black Cat: クロネコ　or 黒猫 (kuroneko, Black Cat). Similar connotations, so it's a simple enough translation. Writing it in katakana will make it feel more like a store name, writing it in kanji feels more like referring to the concept of a black cat, rather than using it as a title. Plus, writing it in katakana avoids having multiple stores with 黒 in the name, giving each a slightly better visual identity.

Mercantile Theory: Literally 商業(の)理論 (shougyou (no) riron), Theory of Commerce. It has the same needlessly erudite feel to it that Mercantile Theory does.

Smooth Saling (I assume you meant Smooth Sailing): 順風満帆 (junpuumanpan), an idiom with a nearly identical meaning to the English one.

Nothing comes to mind for the rest, but if I do think of something, I'll report back. Since you do know some Japanese though, here are some notes:

There and Back: The Japanese term for a round-trip journey is 往復 (oufuku). This is used both figuratively and literally, and it's also used for the inverse - coming and then leaving, rather than leaving and coming back.

Also, notice that in the ones using the particle の, it's optional. It makes them into phrases, without it, they're compounds. For titles, I'd probably omit the particle, except perhaps for the Valkyrie one, since it looks weird to have a compound that includes a German loanword.

Here is a quick list of shop names:

Surely Scrap - A scrapyard that repairs space ships. Based on a planet.

Black Knight Repair - A used spaceship dealership with repair facilities. They can fix it so long as "Tis but a scratch" 

Valkyrie Supply - Do you need a military grade battleship? Then get ready to go on a journey to Valhalla to get it. Valkyrie Supply is an end game fully stocked military supply depot.

Plain Sight - A den where smugglers pass on their ill gotten gains. If you need to hide something, hide it in Plain Sight.

Black Cat - Not every smuggler has a run of good luck... But you can buy more illegal items here if you are feeling lucky.

Murky Waters - Above a muddy river on the planetside, these smugglers get amazing views as they stab people in the back and increase their bounties.

There and Back - You can tell who's been to There and Back. They always look over their shoulder as if you saw the illegal transaction that just took place. Don't be suspicious and you can sell your black market items at There and Back.

Mercantile Theory - A merchant shop that sells legal items and will have you arrested if you bring in any contraban. The only way for you to gain wealth is by shopping at Mercantile Theory.

Smooth Saling - Another non-smuggler shop, Smooth Saling likes the calm riverside view to reminisce on the good old days of sail.

Fed. Up! - A store supplied by the Trade Federation, this shop sells cargo for you to take to the other merchants so you can try and make a profit durring the war.

Aww. Do you have a list of all the store names (in English) and what the store does/sells? I don't mind taking a look when I have the time.

Sorry, there is no deadline but there is also no budget for this game. It's just something I'm doing in my spare time. If people were to help I would only ask that they help when they can. If this game were to be completed though, I would be more than happy to compensate people for their help.

I'd imagine 整船 should be easy enough to pixel - you already have the 船 part pixelled! I'd change the form a bit though, the way you have it is normal for small text, but on a sign I'd imagine they'd have the stroke hanging down from the middle bar in the left part be separate, like this.

Store titles don't need any advanced Japanese grammar, they just need a knowledge of how to make Japuns xP I would love to help you with the titles, it sounds like fun. Is there any payment or deadline for it? I have my own projects to work on too, I can't devote much unpaid time to others. (Also, full disclosure: I'm not great at Japanese either, but I do feel that I can manage a bunch of store names.)

Thanks for the tips! This is my first time doing a pixel art scene with lighting so I just gave it my best shot :P 

I do like your pun for ship shape, I'll give it a try and see how it looks. I only took 2 classes of Japanese so I only know basic grammar and sentences. It would be nice if I could have a translator to help me on this game because I want about half of the signs to be in Japanese.

I'll fix the sign, it indeed does stand out a bit too much and it needs a bit more wear. I've already gone back and added a garage door as well as getting rid of the black outlines.

If you're not going to pun in both languages, you might as well have the sign be monolingual, or make the Japanese part just be the English in katakana. Japanese is so good for puns and Japanese puns are so easy to make even if you're rubbish at the language, I'm apalled that you wouldn't make one xP

Pun example: 整船, a play on 整然 (seizen "neatness, orderliness", the meaning of "shipshape") with the second kanji replaced by 船 (sen "ship, vessel"). Pronounced the same, with the first kanji giving clue to the intended word, but together being a nonce word meaning "neat ship" - which still makes sense!

The katakana of the English would be シップ・シェープ, which is boring and probably too long to fit on the sign.

I think the caution sign on the door stands out too much. Everything else is faded out, but the sign is not. I understand that's the point of caution signs, but it looks out of place.

The light pattern on the floor looks messy. You seemed so busy trying to make it have a nice composition, you neglected to have it make sense xP Start with concentric circles that have the width you want, and position them accordingly. If the bottom few pixels end up dark, that's fine - right now you have a near-tangent of the light with the image edge and it looks bad anyway xP
Another thing about light - unless the air is very dusty or otherwise filled with large particles, the cone of light shouldn't be visible, it should just be the light spot on the floor and nothing else. If the place is meant to be dusty, then you can have your light cone. Otherwise, why not create the compositional effect of your light cone through more interesting means, like highlights on tools in the background? The shop's feeling awfully empty at the moment. You don't have to draw everything out, you can suggest a lot with just some highlights.