I can almost imagine the thought process that went into Jimmy Olsen's famous 'signal watch'. Most Jimmy stories invariably had him getting into trouble, thereby requiring Superman's intervention. Since the editorial powers-that-be had already given the falling-out-a-window gimmick to Lois Lane, they needed a different way for Jimmy to get the big guy's attention.
Hence the signal watch.
Think of it as a hypersonic dog whistle, and you get the general idea. Here, boy! Here, boy! Fetch the bad guy! C'mon! That's a good little Superman....
- NP
