So this is Part II of the DIY Riddler Costume.
We needed to paint question marks on the Riddler costume. So, we needed to make a template: a question mark template or stencil.
We drew the question mark on a piece of paper then transferred it to black crafting foam (you can purchase this at any craft store) so the paint wouldn't soak through - like it would if we used paper as the stencil. Then we put a piece of wood inside the tank top - so the paint wouldn't soak into the fabric and leave black blotches all over the back of the shirt (you could also use aluminum foil or wax paper). We took some black fabric paint and sprayed away.
Here's the process in a pictorial history: