For many years, the term 'digital signature' has meant to me a cryptographically signed digest of message contents, as can be produced by GnuPG or PGP. This provides a high degree of confidence, provided that you've taken efforts to indepdently verify the public key of the signer.
For Google Adsense, a 'digital signature' means typing your name into a box, and recording the time and the IP address of one of your upstream proxies. Somehow I feel that doesn't provide the same level of confidence.
