I've been reading the eBay boards and the PB forum - I am worried about scammers switching my bag with their fake. I've been reading horror stories about sellers not having enough proof and ending up with no bag and no $. I would like to know how I can discretely mark my items. Do I need to buy a special pen? Is the ink invisible? I sold my 1st DB the other day and several of my Coach items are selling. I have leather dog collars, signature handbags, suede bags.... Do I mark them all the same way?