Call-sign/Zap tags are worn in place of a name tape.
Each soldier is given a specefic number that is unique to them and used by them only in the unit.
Name tapes on uniforms tend to get covered up by armor/gear - the tags on the sleeve allow for the soldier to be identified by a specefic number.
A lot of the operations are recorded by video cameras- when the tape is reviewed, the soldiers can be identified by their specific number.
If you are interested in your own personal call-sign velcro patch, I make both 3M reflective and IR patches in a multitude of different camo and colour options:
www.perrozdesigns.com