Okay, get your law school contract textbook out.  This article from WNBC.com discusses a suit a golfer commenced after getting a hole-in-one during a charity event at this golf course.  Signs on the hole said that a hole-in-one would win a golfer an automobile.
But the sponsors of the tournament, will not give the golfer the automobile because their
insurance company said the signs should have been posted at a different
hole: the par-3, 205-yard sixth.