I said they were intended to be visible to those who observe, not to everyone. (There are much longer responses in the Travel Security section of FlyerTalk.) But, in brief:

1. They board during a time when, if any other passenger boarded, they would be arrested for inteference with flight crew. That single fact, alone, means that they can't be undercover. They are already sitting in the airplane, generally (always??) in an aisle seat, almost always (always in my personal observation, but there may be exceptions?) in First Class. So, if *anyone* wants to know if there is a FAM on the plane, it is obvious. (There are reasons why they board early - they need to meet the crew, they need to discuss who else will be traveling with a firearm on that flight other than the FAMs, they need to discuss the "alert" words and signals of the day, etc. Changing this procedure would be a *significant* disruption to airline operations which I can detail some other time if anyone cares).

2. They carry special equipment including a PDA that is allowed to communicate during times when other passengers are not. (Has anyone ever noticed, by checking their own device, whether they have active IR in flight?)

3. They don't drink, they don't take window seats, they don't make an ... of themselves. Those factors, alone, will set you out in some First Class cabins.

4. There are other factors which are not fair to list here.