Hi Leslie,
I see that you want to protect your own designs. No, a disclaimer is not really enough. We rely on our customers' honesty and it's impossible to check what they do with our printables.
I add copyright info to my shop listings and to the printables as a deterrent. I am a member of Acid in the UK (I think thay have links with the US too) which is the next best thing to getting designs registered.
http://www.acid.uk.comI also use Acrobat to restrict printing to low res output on home printers.
Hope this helps!