<RANT>
Personally I think it depends on the sticker as to whether I can appreciate it or not. Bodykits to me are absolutely fine, as dumbass and ridiculous as some of them look to me I can appreciate that someone would put a kit on their car to make it suit them, or look cooler to them (and maybe to others around them). I have no problem with it because people will look at it and think, "Cool/Shit car, Cool/Shit Bodykit".
Now Stickers are the same in my opinion, unless they are advertising something which just isn't the case, in which case I'll agree with Jono that they are very Wank. The number of "claimed" Rally Art Magnas and Evo Lancers I've seen (Even *cough* Evo Lancer Mirages) really does astound me. The problem isn't with someone adding a nice big "Nissan" sticker to their Nissan because they like it and it suits them and people say "Cool/Shit car, Cool/Shit Sticker". It's when they add a "NISMO" sticker to their stock shithouse pulsar, and people look at it and go "Wow, NISMO Pulsar...Fuck NISMO is shit, Check out my fully fukin schmick SS Common-Whore with Chrome dinner plate mags, ass scraping the ground and gold fluffy dice that make you wanna scream Yeeeouuuch!" Then whoever they're with looks at the Pulsar and agrees.
If you've got it and you want to then flaunt it. If you haven't got it then get your dick out of your hand. Your mum probably doesn't want those stickers all over her car anyway.
</RANT>