“The other day, there was this line of people out in front of the shop,” said Mark Mahoney, the owner of Shamrock, who has his own share of celebrity clients like Rihanna and Johnny Depp. The line included a gaggle of 20-something women and an older man in a suit. “I was like, ‘Is that a professor and his class?’ ” he said. " ‘Is this a field trip?’ ”

“But it was Woo making appointments for next year, and people wanted to come in person to do it,” he said, shaking his head in disbelief.

To hear Mr. Woo tell it, he is simply following a tradition taught to him by veterans like Mr. Mahoney, who gave Mr. Woo one of his first legal tattoos at 18. At this point, Mr. Woo has so much ink — an anchor on an earlobe, the word “cope” written in cursive on his neck, a 1952 photograph of his Taiwanese grandfather on his arm — that he can’t remember what, exactly, was his first legal tattoo.

“I think it was some birds,” he said, shrugging. “I forget.”

Growing up in a suburb of Los Angeles, Mr. Woo became fascinated by tattoos at 13, around the same time he stopped taking violin lessons. He and his friends would experiment with ink and needles after school. It became competitive when one of his friends got a professional tattoo. “I just wanted a lot of tattoos,” Mr. Woo said. “I wanted to be covered in tattoos.”

After high school, he tried community college but paid more attention to partying, skating and going to concerts. He was managing a clothing boutique and toying with the idea of creating a skateboarding-inspired clothing line when Mr. Mahoney suggested he apprentice at his shop.