From the Shirtpunch.com's interview with the artist:
"Question: What inspired this design?
Answer: Mario's mustache reminded me of the samurai helmet mustaches! Since I have always been a huge fan of samurai armor, and Mario 64 also happens to be one of my greatest time sinks as a kid, it just made perfect sense."
About Shirtpunch.com: It's simple; ShirtPunch is your home for limited edition, pop culture tees... but there's a twist! We only offer one shirt every 24-hours, and they're always only $10.