Identity tapes were a small, portable form of identification used by Federation citizens during the 23rd century. Identity tapes were typically used by citizens engaged in deep-space travel that might take them out of regular contact with the Federation. The tapes provided a form of verification and guarded against identity fraud over long-periods of absence from society, during which time their identity might be assumed by another individual. Identity tapes included bio-metrics of the individual and could be matched to records of that individual maintained in the computer of a starship or starbase.
Carter Winston supplied his identity tapes to Spock according to Starfleet regulations when his vessel was discovered by the USS Enterprise after he had been missing for 5 years. (TAS: "The Survivor")