You do realise that you can just google the term Tramp Stamp,don't you?
Anyhowu2026
It's a tattoo on a woman's (generally) back,on the upper pelvis.
I've not heard the term much in recent years but it was very common 10u201315 years ago as it seemed like this was the type of tattoo (not this design specifically) that every woman with visible tats seemed to have.
I guess it's commonness came to be associated with trampy/boozy/slutty/skanky (choose the negative pronoun of your choice) women and the outfits that they would often be wearing which would have this type of tat on display.