As to me, a signed cel has more value.
But I agree with almost everybody here tosay 
that it would destroy the beauty of the cel 
itself...
I had the opportunity to make some cels signed 
and choosed another option: I got my signings on 
the sketches!
I don't know if you will agree with me, but I 
think it's the perfect solution. 

LMK what you think about it.
Cheers

Almathea