"a black Velcro strap covered in black cork. The cork signifies the protective coating used as a boost protective cover during Saturn V launches. The markings on the cork obviously make each one unique and I’d call it a really thoughtful add."
I'm only quoting these articles because I wasn't sure myself but briefly remembered it was cork, but not the location of where it was on the Saturn V.
From Mono-chrome watches:
"An additional Velcro strap in blackened cork with golden marks is also included. “This innovative design is a salute to the Apollo-era “boost protective cover” - a fiberglass structure covered with thick cork ablator which fitted over the Command Module like a glove, keeping the crew of the Saturn V rocket safe from the intense heat produced at launch,” says Omega."
The command module was covered with a shiny cover. The Mylar of the cover was attached via the cork. You can see it stripping off when the CM was being recovered.