Here is a guitar pedal supposedly signed by all three members of Nirvana that was posted on a Facebook forum. Here is the story of how he obtained it.

 Kurdt did use the pedal yes. I didn't meet him (unfortunately)  I bought it from the guitar player of dinosaur Jr. He had cancer and he was selling everything he could. With it he gave me a hand written letter of the pedals history. Him and Kurdt exchanged this pedal a few times apparently. He was the one who got it signed. I have met Dave G however and he remembered and also authenticated it for me!

He used it circa 85-88 never used it to record any records. He did however record the 85 demo "class of 86" as Fecal Matter with it. So goes the "story" But I'm sure you knew that.

Firstly all 3 autographs does not look good to start with. Secondly his story of how he obtained it just does not checks out. The guitarist from Dinosaur Jr  whom he got this  guitar pedal from had cancer and has to sell everything. Last checked all the guitarist that were in Dinosaur Jr are alive and healthy. If this was from the Fecal Matter period which is 1985-1986 . Krist Novoselic was not in the band and Dave Grohl was not with Nirvana till mid 1991. Both Krist and Dave autographs examples are from after 1992 if they were authentic.

I am surprised that it is not on the bay  yet!!! :D