I personally don't mind them. I don't have one 
signed yet, but I will in the future. I am 
saving for the dream cel I want signed as we 
speak. I personally wouldn't sale a signed cel 
that was for me.

When I went to a convention last year, someone 
got their OP DBZ cel signed by one of the voice 
actors and he knew not to sign on the cel 
itself, but to sign in the blank part of the 
celloid.

I wouldn't mind if the blank part got signed, 
but not the painting itself...