The rocker revealed the true meaning behind the ink in a second post.
Barker posted a video of himself self-inking the new body art onto his right thigh. The message reads, "You're so cool!" with a small heart next to it.
Shortly after posting the video, Kardashian commented on the post, "You’re so cool!"
Fans went wild, speculating in the comments that the message might have been written in Kardashian's handwriting.
Barker later gave more insight into the meaning behind the tattoo. The message actually comes from the 1993 film, True Romance, the screenplay of which was written by Quentin Tarantino. The line comes from Patricia Arquette's character in the film and the handwriting is her own after she writes it on a napkin in the film.
Barker shared more pictures of his ink along with still shots from the film, captioning the post with another line from the movie, "I like you, Clarence. Always have. Always will."
The Blink-182 rocker has said in previous interviews that his favorite movie of all time is True Romance, and Arquette's character in the film is named Alabama -- the same name as his daughter.
Also of note, earlier this year, Kardashian shared screenshots from True Romance, of which Barker commented, "You're so cool."
While he may not have gotten ink in his girlfriend's honor, Barker and Kardashian spent their weekend together in Las Vegas, watching the UFC 260 fight between Francis Ngannou and Stipe Miocic. The pair were seated next to Barker's friend and collaborator, Machine Gun Kelly, and his girlfriend, Megan Fox.
"Kourtney and Travis are in total lust over each other and she doesn’t regret going public with their relationship at all," a source told ET earlier this month.
"The relationship was a long time coming because the attraction has always been there on both sides," the source added. "They love the fact that they have a true friendship and bonded that way before taking anything further and making things romantic."