Russell W. has left a new comment on your post "Name the sing contest from a reader":
A curious twist to the 'song fragment' contest: playing a clip of a given record backwards. Not all that easy if the snippet comes from something other than the song's hook.
This brings to mind a couple more contests from way back:
ZAP: The caller has to guess which of the station's call letters are replaced by a sonovox "ZAP" ... versions of all four combinations would be randomly placed onto one cart, and after the caller makes their guess, the next cut is played. If it matches, they win.
A small station in Selma, Ala. used to have a contest called "What's Cooking?" -- the jock would start reading one ingredient, adding another one after each record, and the object was to guess what the recipe was. I have a clip of one, and the callers had some awfully creative guesses.