It actually can be related to a couple of possibilities, depending on who's saying it, or who's got the sticker. The usage is a take off on the advertising campaign "Got Milk?" Got a Uke could be a...
An uke is the guy who is on bottom in gay sex. Sama is an ending ( Like Sesshomaru-sama or Light-sama) that means master. It is also used when referso ones parents (oujo-sama)