I don't add branding to my printable designs - at least not to the design itself. I figure that as long as the design I'm selling them is personalized (photo, names, dates, addresses, etc), they've paid for it so there's little chance of them taking that design for other purposes. When I give them a JPG, it's high-resolution for that size only, and if I send them a PDF, it's HQ without editing capabilities so if they did open it in Illustrator, they'd have a hard time manipulating it.
Now if I were selling printable PDFs that weren't personalized, then I would put a Copyright notice on it.