Ok.. this is a fun one. We have a 1948 gmc flatbed fc303. It used to have an old mechanical turn signal on it, just like your hand signals.

Where on God's green earth could I find another one? Here's a picture of the holes on the side of the cab where it went:

http://i271.photobucket.com/albums/jj155/turpentyne/signal_mount.jpg?t=1199889910