More to it than that (Score 1)

The U.S. E-sign legislation requires that

• All parties agree to accept a given digital gesture as a valid signature;
• The entire text of the agreement that was digitally executed be preserved in verifiable original form; and
• The original executed document can be reproduced on any signer's request in a reasonable amount of time.

In practice, the form of the signature is the least onerous requirement. A simple "I AGREE" button is as legally valid with or without a sophisticated PKI signature, e.g., from VeriSign or Thawte. Entities that want to offer legally binding digital agreements spend much more time focusing on the storage and retrieval requirements.