For a private, scheduled photoshoot, just take it off and set it aside. Don't forget to pick it back up again when you're done.
For a quickie hallway shot, have your badge SECURELY clipped/pinned/ziptied to a side of your costume (belt height maybe) and practice a pose that turns the badge away from the camera. Or if you have a big prop like a shield, secure it to the inside of your shield.
If you have a couple of pre-determined poses for your character, and can pull them off on command, it'll make your quickie hallway shots much more interesting. Exaggerated poses and facial expressions make for interesting, fun photos. Practice these poses in front of a mirror, and figure out where you can put your badge so it won't be distracting and right in the shot.