Many production cels don't have the holes because
they were on an extra strip of plastic.
Else, it's quite easy to make holes if you
realy want to...

Signatures that can be removed by just "looking
too hard at the cel" are useless. Same if it's
on a sticker (that is often given separatly).
Or on the back of the cel where it can be 
removed/hiden quite easly. I saw very nice 
Miyazaki cels... It was just writen on their
back "sample". Don't you think it can quite
easly be removed with a little water/spirit 
without damaging the cel ? Or hidden by a new
layer of paint ?

As for not signing... it's the fashion currently,
isn't it ? Sites like Ebay claim they don't have 
any responsibility if people sell illegal things
because it's writen that they shouldn't.
Providers doing free email claim they don't have
any responsibility if their users do spamining :
because it's writen they shouldn't.
Sites like napster claim they don't have any 
responsibility if their users copy and 
redistribute copyrighted musics : because it's 
writen that they shouldn't.
...

All write what their users/customers aren't 
allowed to do with their services. But none
try seriously to find a solution.
Either they are very naive, beliving that
everybody will follow what they say and don't
abuse. Or it's just a way of trying not to
assume their own responsibility while seemingly
looking nice.
The wake-up may be hard for some if one day
they have to face their own responsibility...

Cheers,
Yann Stettler