It has some flair of electromechanics to it, but what exactly do we see here? It is at the centre of composition, so we should have a clue how to interpret it. (maybe some inscriptions or background) Also it is slightly off-center (see by | between - and +). Letter "D" would look better if it's corners were not 4 pixels like now, but 3 pixels - experiment and you will see.
You're right that simplicity is good, if treated right, it makes visual message very clear.
Welcome to PixelJoint, hope you will not be turned off by some critics!
Mmm. You're right. i try to center it and the " d " could be better. Thanks for the comments.