Nancy Drew tattoos
Some hobbies a daughter picks up from her father, and some hobbies a father picks up from his daughter. We think in this case, it was the daughter who suggested they get matching Nancy Drew tattoos. The father is probably a fellow fan of detective stories and spy novels, and so it made sense for them to put in ink their shared hobby.
Guess we can say we solved the mystery of the tattoo, huh? This girl and her father got the ink in the same spot on their arm, and it looks great on both of them. If you grew up reading detective novels and solving mysteries around the house, it seems like this might be an appropriate choice of tattoo.