I've actually made the decision to *not* 
watermark my cels.  I think the watermark 
detracts from the image, and since I have 
physical possession of the cels, there is no way, 
other than breaking into my aparement, that 
someone can "steal" them from me.  I figure I 
don't own any licencing rights to the images 
either, so I can't really made any demands about 
their use.

Just IMHO, in case anyone cares. :)