Anyone had warranty work done on a Sigma? If so, did you need the warranty sticker? I just bought a Siggy 120-300 and there was no warranty sticker in the box. I sent a note to Amazon about it and they said don't worry, I won't need the sticker if my lens needs warranty work. I'm not too worried as I have never had to send in a lens or body for warranty work, but still, this is a pricey lens, so I want to be covered.