I have never heard of any airline ordering its employees to pay a bond in the US. Some high level managers sometime sign a non compete clause which is also highly suspect in a court of law but I have never heard of any airline "offering" a bond to its pilots. Must be some fly by the night operation just trying to make a buck off some dumb unsuspecting pilot.
Non of the majors give it, non of the commuter that I know off (I could be wrong here though) give a bond and non of the frieght dogs do it either (Fed Ex, UPS, Airborne).
When a comany gives you a bond I would be very careful of what kind of operation I was getting into. Why would an airline do that and what are they trying to prevent by their actions or even inactions?