Made all the more secret by having it tattooed on his face, of course.
Specifically, the approximate English sounds for these five characters are I, M, H, T and P -- Imhotep.
And as for their rippling pecs:
... they add a reference to needing to silence something hidden in the desert. It actually makes perfect sense for a secret society whose job is to keep the secret of an evil, hidden mummy destined to rise again.
The problem is that the movie portrays these guys as having the tattoos while Imhotep was alive.
In other words, before the guy was dead, or a mummy, or cursed to return, they were just a bunch of pharaoh's bodyguards, hanging out with Imhotep while bearing written declarations that they were going to eventually have to kill him and guard his cursed corpse for the next 3,000 years. So we wind up with a scene where the bodyguards all blunder into a murder scene, and are shocked by an event their own tattoos had warned them about. Great job, team!
That ancient Egyptian tattoo artist surely had some tough questions to answer.