If you're willing to pull off a scam, it's too 
easy to simply make up numbers to put up at the 
top of the cel -- and ta da -- instant production 
cel. What's to stop a person from doing this? Not 
only is it easy, but it's profitable too. 

At this point you'd have to find the sequence and 
compare it to the finish work, maybe ask people 
if they might have cels from this sequences, and 
even then the question might still be up in the 
air.

Check out the case of SStrunks. Some of his cels 
were only identified as fan cels through the 
signature. The Duo cel fooled me. God bless the 
person who was honest to sign the things and 
claim it as her own. 

I don't know how a signature can mar a cel. If 
it's off to the side, it's not going to draw 
attention away from the piece. I think if you're 
good enough to paint like a pro, you should be 
proud to have your name associated with a piece 
of work.