Unless they're blocking vents or something, just leave them. They're good to let you know the age of the helmet (which should be replaced periodically) and if you have something obscure and you race, it'll tell the officials that your helmet is CPSB certified. That may not seem like a big deal, but when the Cateye Whisper Lite (the honeycomb helmet) first came on the market, it wasn't rated by the CPSB, only the Euro agency, and so couldn't be used in US races. It's since been certified, and is becoming mainstream, but it can come up from time to time.

Beyond that, who cares? I guess as long as it's not pulling off chunks in your hair or stuck to the sticker, then have at it. I wouldn't waste my time messing with it though.