I work in a manufacturing plant and a coworker who lived right down the road (most live 30-40 miles away) would leave his bike inside the building out of the way near my equipment. The problem wasn't thinking someone would steal the bike, I don't think anyone would do that from inside the building with so many people roaming around (outside on a vehicle is another matter, I'll have to try to figure out how to lock mine to the car on a trunk mounted rack when I get a decent bike.) The problem for him was more, he would find it on top of the box trailer that was docked inside the building or he would find it locked to a materials rack with some other lock that he didn't have a key for, etc.

We would only do that to a good coworker friend, as he was a good friend, and always got it back to him before we left (several of us up front worked 8 hour 5 days while he worked production 12 hour shift.)

It's just the plant horseplay that happens. You should always expect to find your personal stuff messed with. People have come back from lunch break to find everything in their workspace cleaned out and hidden, hanging 50 feet up in the rafters, etc. The more you made a fuss about it, the more you got messed with.