A lipstick mark left by an old woman who might or might not be a grandmother.
Eww! That granny stamp was moist!

Did you just get granny stamped?
by Racoons In A Trenchcoat October 17, 2019
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This is what tramp stamps become when these hotties hit their 60s and 70s. A tattoo on the lower back of a grandmother (possibly a GILF now).
That old lady must have been hot in her day, I'm sure she has a granny stamp to prove it!
by LeGogh February 20, 2010
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