I watermark high end cards in photobucket cause there's so many people stealing images for fake eBay auctions, not sure about jersey images but if any doubt, watermark.
I dont watermark anything. Have just set the site so it is harder to save the images off it. At the end of the day if it isnt your image it will be someone elses they use.
Just one of those things where I'd rather people NOT pinch my images, (yes, despite them being ONLY Harris', Matty!!!), but it affects my entire gallary site, so ANYTHING I upload, including Trade Bait, box breaks, etc, etc, they all get watermarked.
If I can do my bit to stop people from using others' images on ebay, then I think it's a start.