I want them about 2.5" high and want to add over 100 of them in a brick pattern to the jacket and pants. If I were to cut them out of fabric it would have to be poly/cotton to match the suit which would be impossible to do with a consistant degree of accuracy.
Your best bet would be iron on transfers. Just print out a sheet of the question marks, cut them out, and you're good to go. Any kind of sticker is likely to peel off due to movement.
I'd have to agree with precious, Iron transfer is the way to go. I think any type of fabric sticker is going to peal if you don't sew around the edges. I make alot of custom biker patches with adhesive backs. They all curl if you don't sew for security. Just my opinion. Good Luck!