guitars

Oh yeah! The "secret" "third pickup".

https://en.wikipedia.org/wiki/P.A.F._(pickup)

A P.A.F., or simply PAF ("Patent Applied For"), is an early model of the humbucker guitar pickup invented by Seth Lover in 1955, so named for the "Patent Applied For" decal placed on the baseplate of each pickup.[1] Gibson used the P.A.F. on guitars from late 1956 until late 1962, long after the patent was granted.[1] They were replaced by the Patent Number (Pat No) pickup, essentially a refined version of the P.A.F. These were in turn replaced by "T-Top" humbuckers in 1967, and production ended in 1975. Though it was not the first humbucking pickup ever, it was the first to gain widespread use, as the P.A.F.'s hum-free signal, tonal clarity, and touch sensitivity when paired with overdriven amplifiers made the pickups popular with rock and blues guitarists.[2] The P.A.F. is an essential tonal characteristic of the now-famous 1957–1960 Gibson Les Paul Standard guitars, and pickups of this type have gained a large following.