I've run into a slightly different issue. I want to use an equal sign ("=") in my signature. The form accepts the character and displays my full signature on the picture, but I happened to save my design. When I look at my saved design, the "=" and everything after it is missing!
There is a bug is saving my signature, but I have know way of knowing if the same bug will affect me when I try to check out. I don't know what to do about it.
I "chatted" with a Motorola rep. He said that only letters and numbers will be printed. In that case, it's weird that I can save lots of different punctuation and symbols, just not a "=".