Drake and Rihanna: If A Kiss Don't Confirm It, A Tattoo Will

Drake and Rihanna are becoming more and more of a legit couple with every passing day -- Rihanna just sealed the deal by getting a tattoo for Drake ... TMZ has learned.

Sources tell us Rihanna got inked Wednesday night after Drake's concert in Miami with a little shark on her ankle.

Sources say the shark tat symbolizes Drake and RiRi's aquarium date earlier this month, where Aubrey took his new girl to see some fishies in Toronto. He bought her a stuffed shark doll that night, and now she's paying him back by showing some permanent love.

We're told the tat was done by celeb tattoo artist Keith "Bang Bang" McCurdy and our source says Drake got some ink as well.

We hear Drake is super down with her shark tat ... obviously.