i think its a bit bollox to be honest. in theory its a good idea but 'back in the day' club gti was the only club around. now with the whole internet community thing i can't see it having the same effect. i wave at loads of other vw's or give them a flash/toot of the horn etc. especially if they have a 'modified' one as chances are they are 'into the scene'.
on the way to jv's on friday i had a lupo give me the flash thumbs up etc on the m25 which was cool. the fact that we were both in nice vw's was all it took... not a sticker.
also gibby on the way to e38 last year, it being the same weekend as the vw action one, i beeped and waved at loads of aircooled vw's and they all looked at me like i was some chavvy boy racer!
it is a good idea but at the end of the day if you're flying down the road would you notice a sticker? if you're driving around slowly or sitting in traffic then it should be obvious if you're a vw entheusiast rather than 'just another owner'.
also like jv said all it would take is someone to start a forum to connect all these sticker owning people and all of a sudden its another club/forum/community. also who will make these stickers? does that mean they are in charge?
at the risk of being a grumpy old man (i'm thinking of trademarking that) too many variables to make it work. for starters all the people who don't like the 'winning' design will be pissed that theirs didn't make it!