A term used to state a claim of dominance of a female being through the act of sexual intercourse. The term refers to the metaphoric description that the male has "signed" his name on any chosen part of that particular female's body, primarily the stomach area or lower back, with his ejaculatory fluid.
"Nah man, its all good, I already signed that shit months ago at that one party."
"Dude, you better sign that shit tonight"
"Good luck with signing her up after taking her out to dinner"