I'm with carrieg, Iron Freezer Paper on the back of the fabric area you want signed. It makes it stiffer and easier to sign, plus it comes off easy to. :) Personal preference on the blocks though. I would precut so that the person could pick which color they wanted, or if it's all the same color you would have a signed and unsigned box. (no worries about the one person to tipsy to pay attention to any carefully drawn lines)