I think that the "if the shoe was on the other foot..." analysis is a good one. Then consider that people don't necessarily use their property all the time. Strangely enough, the Austin ordinance allows the city to remove a bicycle after only 48 hours! That's not NEARLY long enough.
Generally, I try to hold myself to the highest standard. If I can see any way that people could disagree with what I'm doing, then I don't do it. I always assume that someone is looking. Having one's stuff stolen sucks, and I never want to cause that hardship to anybody.
How many people here have had formal training in ethics? I've had one course each at the undegraduate and graduate levels.