Transponder module with antenna

Sailing ships of old would carry various flags(colours) to indicate their status, but would not necessarily show most of them unless they were in fleet or with an ally.

The Jolly Roger was raised on an attack run to scare the victim ship into surrender.

Running a neutral identifier would be a choice to avoid engagement or other identifiers when in difficult territory.

Verification codes could be required with an identifier to allow the use that identifier.

Displaying your real identifier could be required when docking at a station.

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Having your transponder off (intentionaly or otherwise) could have other faction-related impacts as when you're docking at a colonization authority base (for example), they might question why your transponder was shown to be off at some point along the trip.

This would obviously require some sort of additional interactions (NPC space cops or whatever), but that would tie into factions in general. Break the colonization authority up into sub-factions like 'colonization security, who have their own missions or colonization emergency responders (CER) who go rescue ships or stations in hazard. Heck, they might even rescue you if you're lucky with a ship out of fuel and drifting towards Delfos.

Currently, it seems to be implied that your transponder is somewhat built into your antenna. Being able to separate that and shut off or manipulate the output to appear to be part of a different faction would be a fun additional layer to ship to ship (or ship to station) interactions.

The renegades might try to spoof a legitimate ship signal to get close to your base, and there should be some method to detect a spoofed signal. Ideally something that is never 100%, but increasingly harder to spoof as your tech tree advances. Same in reverse, if you're trying to spoof a signal to approach a base, some basic renegade outpost should be easier to fool than an advanced military facility or battleship.

Pirate station can offer transponder change service, so you cannot do it on the fly and change back whenever you like.

I have been inspired by the previous comments.

Passage codes that you can purchase from any space station that have a limited duration.

That is a code to confirm the validity of a transponder status.

You could buy faction membership code for a week, month or longer.

You could buy a temporary transit code, trading guild pass or a mining license for operating in controlled territories.

The right to purchase a code would be determined by your current record

All of these codes would grant favour of some sort beyond normal status.

I am not sure how the transponder of your vessel and of your character comms system would relate.

Hmm...I've been wondering how this would apply to online games, in a way that admin would fine fair.

I say keep it (antenna and transponder) together, for coherence sake, and enable 3 transponder outputs:

1. Open channel: This is what you decide it broadcast when, well, broadcasting generally.
2. Response channel: This is what you decide it broadcast when a scanner or another transponder 'interrogates' you. Maybe a hard target lock does it too? Just more information you decide to add, that is publicly available.
3. Encrypted channel: This only broadcast what you have in there, when it receives a 'password' you set up. Could be general or response channels, just now encrypted. For use with friends/factions.

Now, the tricky part is spoofing, and a fair way for players to engage in that.

One way I've been thinking on, is (this is the in-game logic) by having a unique encrypted identifier attached to each antenna when it is made. This is set up so that only certain people can access it, if they get the license to access that encryption, i.e. police/base security/bounty hunters. Now you the player can remove that, but now when you are scanned by someone with that license, they will know you have a tampered transponder, since the encryption is gone.

Use for online play: Your character name for the server is that 'encryption' on the antenna, you can't change the name, only 'remove' it, unless you build a new one that will 'repopulate' the encryption again. So, only applies when you are actively trying to be sneaky, or incognito. If you want to go back to normal, say a station or player base requires it for security, just build a new antenna, which 'resets' your status to those who can interrogate for that special 'hidden' 4th transponder response.

Application: You are a bounty hunter, you see a ship fly by with no signal. You interrogate, no response. You use your bounty hunter license to interrogate, and get back a 'tampered' flag. This player removed his transponders 'VIN', essentially, and the antenna is powered on, but not broadcasting, and the entries are all blank as well.

This also opens up the whole concept of hacking to gain access to remote (hostile) grids. This could be one of the things you could do, but a full on electronic warfare/transponder block could include spoofing signals, but also act as a firewall (incoming) and perhaps a way to remotely gain some access to remote grids. Not to the point of taking over the remote grid, but shorting out some turret control or something might be a fun aspect.