Banks don’t even bother verifying signatures on checks less than $30,000; it’s cheaper to deal with fraud after the fact than prevent it.

Notes Bruce Scheneier in passing, in an essay which starts from the oddity of fax signatures and goes on from there.

That approach presumably relies on counter-parties to detect and report that they have been defrauded, which makes a pretty important difference from government services – but the questions it prompts are interesting and important:  what could be the role of post-event security in government services?  And what would be needed to make it work?