metalink form factor
This. Apply form factor to the cheapest comm-link you can buy. It's not going to stand up to any kind of serious examination. But if a deckers looks for it, they will see that it's icon is there, and that's the whole idea.
If you wanted to spend some money on it, and get tricky, you could get a better link, then add a dongle on it to give a sleaze rating, it would be stupidly expensive as dongles are like raiting^2 cost, but it could take someone a couple actions to find it and figure out what the heck it is, depending on how cautious they are.