Electronic signatures and watermarking?

["Spencer, Mark" <mspencer () evidentdata com>]

On business documents (those that still live in the paper world) where
public/private keys and signature verification are unavailable, is there
a way to make an electronic signature (a handwritten one that has been
scanned in) more secure?  Possibly by watermarking?  Anyone can scan in
a handwritten signature and paste it into a document, but I'm curious
about how one might watermark or otherwise secure it.

Thanks!

Mark