tramp stamp
n. A lower-back tattoo, particularly on a woman who ensures the tattoo can be seen by wearing a short top and low-rise pants.
Most fashion faux pas and bad hair cuts are easy to put right. When it comes to tattoos, however, erasing the past is not as simple as ditching those ill-advised bags, sunglasses or shoes. The tattoo removal industry is, however, burgeoning, thanks in part to the legions of women who flocked to copy their celebrity heroines such as Angelina Jolie and Cheryl Cole and have so-called "tramp stamps" imprinted on their lower backs.
—Andrew Johnson & Joe Kenward, “Ta-ta to the tattoo? The rise and rise of removal,” The Independent on Sunday, September 06, 2009
Wagner said people get tattoos because, like Race, they are either true art connoisseurs, or they want to look cool. … He also said he's not sure what led to the "tramp stamp" craze, meaning abstract tattoos on a woman's lower back.
—Mary Maraghy, “Riverside tattoo artist promotes artistic nature of the business,” Florida Times-Union, August 08, 2009
2003 (earliest)
Her pants were so low cut, you could see her tramp stamp.
—Vegas, “Tramp Stamp,” Urban Dictionary, March 22, 2003