The MND agents need to stay covert, if they want to succeed. Therefor the Directorate ordered, not to use an universal callsign in front or after the agents call sign. All of the agents are constrained to use aliases, when they operate in enemy territory, to prevent casual detection by the enemy intelligence service. However if using a Rheinland Corvette, the agent is ordered to use a unique name flag, which indicates him to be a member of the MND. This flag must be <needs to be decided>
This says only about naming. I dont really think it has anything to do with Tags.