Proof of Identity--All Things Change

Once upon a time, the signet ring and the seal, as in the Great Seal, were the proofs of identity, and were the means of authenticating a legal transaction.  Then, as literacy spread, the signature was added, eventually replacing seals and signets for all but the most official transactions.  (Go to have a document notarized and she has a seal and will emboss your document.)  But all is changing.  From a Timothy Lee Vox post, on how Europe does debit cards better than the US:

Unfortunately, signatures are practically worthless as a security measure. If you don't believe me, try scribbling randomly next time you're asked to sign a credit or debit card receipt. I've been doing this for years and I've never had a store clerk decline the transaction because my signature didn't look authentic.
The rest of the world is way ahead of us on this. Over the past decade, the United Kingdom, Canada, and Australia — just to name a few — have switched to PIN-based authentication, in which customers identify themselves with a four- or six-digit code.