Today's episode had the Shropshire Slasher recast as the Smasher, and whenever he appeared they played a four-note "theme music stinger" and I'm very surprised they didn't have the characters recognize it and thus be warned that the Smasher was around. (Maybe they did and I didn't notice it.)
It was the first four notes of the theme from the old radio show "The Whistler" and I have no idea whether or not they used it knowing what it was. I'd have to dig out a copy of Deduce, You Say! and watch it again.