Hi Tori,

Not sure, what "common/accepted" business practices are, but creating a digital signature is not a big deal, if you have a WACOM tablet, digital pen, and Photoshop. You'd create a "brush" from your signature. Scott Kelby provides step-by-step instructions in his Photoshop "[insert version] for photographers" books. In these he also describes how to create digital water marks.

Cheers!
GG