In late 1957 a black sticker with gold lettering was applied to each pickup's underside, that read "PATENT APPLIED FOR." Over time the Patent Applied For sticker present on these pickups has evolved into the acronym P.A.F. as a way to identify pickups with this sticker. The patent for Gibson's design was eventually issued on July 28, 1959. The acronym P.A.F. is also sometimes written as PAF leaving the periods out. However, in 1978 the word "PAF" was registered as a trademark by DiMarzio. This registered trademark should not to be confused with original P.A.F. acronym used to describe the original vintage pickups made by Gibson and the subject of this article.