I've seen Sepultura's guitarist put a bunch of what looks like stickers on his guitar, like the weed plant one..
I've done it before, and it just interfered with my pick ups. Of course..

So are they stickers or something else? Because i've seen him actually stick those on his guitars. (For example the Jackson Flying V he owns)
Interfered with your pickups?!
I put stickers right on my pickups and it didn't alter the sound at all.
I don't understand what you mean.

But yeah, I wouldn't put stickers on any decent guitar, it looks tacky, and if you want
to take it off, there'll be a sticky mess stuck on the guitar afterwards.