The 45-year-old musician was also photographed shirtless in Hollywood on Thursday while working on a new project, and the tattoo is visible above his left nipple. Barker and 41-year-old Kardashian have been linked since January and were longtime friends before their relationship turned romantic. Late last month, fans also speculated that Barker's new tattoo reading "You're so cool!" with a small heart on his right thigh was for Kardashian.
Meanwhile, Barker isn't shying away from flirting with his girlfriend on social media. On Thursday, he left a comment on Kardashian's Instagram post, in which she quoted Ariana Grande's lyrics to her hit, "34 + 35." Kourtney wrote, "Watchin’ movies, but we ain’t seen a thing tonight," to which Barker replied with the smiling face with horns emoji.
A source tells ET that Barker and Kardashian are "so into each other."
"They act like teenagers who are in love," the source says. "Their chemistry is crazy and everyone around them can see how cute they are together and how happy they make each other. Their relationship has been fun, easygoing and natural and is the real deal."
"This is the happiest Kourtney has been in a while and her family is thrilled for her," ET's source said. "Kourtney and Travis' kids get along great and all have the best time together. Kourtney's been trying to keep their relationship as private as she can on social media, but they're both super into each other and cute together."