Star Trek: 10 Things You Didn't Know About Combadges
9. Combadges As Identification
Every combadge had unique markers that could be used as personal identification.
In the Next Generation episode Drumhead, we learned that the Enterprise's computer could actually tell who was using a console at any specific time by interfacing with their combadge ID. Additionally, the episode The Hunted revealed that combadges from this era also included a record of their assigned user's fingerprint data, which allowed access to be restricted to them alone. This security feature prevents stolen identities and is very similar to fingerprint scanners on modern smartphones. It's also very likely that an officer's combadge could be used as a more futuristic form of real-life military dog tags (or ID tags) that were used to easily identify casualties.
As most fans already know, Starfleet transporters can also lock onto specific people using unique markers in their combadges, and there are probably many more forms of ID included in them that we haven't yet seen on camera.