From The Old School Dictionary Of EduSpeak

Trampstamp: (n.) A certain type of tattoo often seen on adolescent/young adult human females. This tattoo is most often placed on the small of the back with the intent to exhibit the tattoo (through the use of short tops such as the one illustrated) while walking through the hallways (and sitting at classroom desks) of high schools and colleges. Also known in some circles as The Mark of the Whore.