In all honesty, I am not really sure where the term joker ticket came from.  However, I do know that some people in the fashion industry refer to price tickets as joker tickets.  If you are not familiar with a price ticket, that is the small tag that you find hanging from clothing that contains pricing.  The price ticker (or joker ticket), also typically contains a UPC code, department number, style number and a few other bits of information.

The joker ticket is often attached to clothing by a swift tack or tagging pin.  They are attached with the help of a tagging tool.