I've left my fixed "free-locked" (front wheel krypto'd to frame) for short periods many a time, back when I was messengering that's what everyone did. Of course, it is a little different when a person is leaving it out for long periods of time. And people walking around with a bike locked to itself kinda standout. Good way to get yourself arrested.

Leaving a note, I suppose I could see doing that... taking property that belongs to someone else, for whatever reason, we have other words to describe.