Within the Army's military police is the Criminal Investigation Command. They're like NCIS for the Army (the real one — not the TV show). They conduct investigations, collect criminal intelligence, provide forensic laboratory support, and, occasionally, they're assigned to a unit if they suspect something is wrong.
If CID catches wind of serious misconduct, they'll insert an agent into a unit through which they'll observe what's really going on. The chain of command might know what's going on, but no one in said unit is aware.
Now, we're not telling you this to put you on guard at all times — that'd be crazy. You should only suspect someone is secretly a CID agent if they show any or all of these signs.
Then you should absolutely be suspicious.
1. They're optimistic about the unit.
It's impossible to show up to morning PT both sober and ready for the day to begin. Anyone upbeat and cheery is not an organic piece of your unit.
2. They claim they don't know how to print out their ERB (or don't want to).
Their ERB is a dead giveaway. Every soldier loves bragging about themselves. At every possible moment, we love to remind people that, "actually, I have four certificates of achievement, not three."
Anyone who's not willing to engage in a proverbial pissing contest is clearly a 31D and not an 11B.
3. They don't brag about their previous unit (or claim they didn't have one).
Speaking of bragging, everyone also sh*t talks their current unit because the last one is always better.
Beware if you ever hear the phrase, "well, I mean, my last unit was okay. Nothing bad, but nothing special." Obviously, their previous, nondescript unit was CID.
4. They're unwilling to do dumb sh*t with you — but want to watch.
What kind of grunt isn't willing to throw their entire career away at a moment's notice because their buddy said, "hey, bro. Watch this"? CID agents, that's who!
Chances are, they'll be sitting there with their beer, taking mental notes to use against you in court.
5. They're always asking how your weekends were.
Immediately after a four-day weekend, normal people will make small talk by saying, "how was your weekend?" We're not here to burst your bubble, but this isn't because they actually care about what you did. It's a hollow gesture. Nobody actually cares that you just stayed drunk in the barracks, playing video games.
If there's even the slightest note of sincerity in their voice, it's a CID Agent trying to get you to spill the beans about what you did.
6. They're a lower enlisted who actually knows regulations (other than the loopholes).
If pressed on the spot, every response to any regulation should be, "Ah, crap. It's, uh... AR-6... One sec..." followed by an immediate Googling of the answer. The only time a troop should be able to spout off regulations off the top of their head is if they're an NCO.
If they know the regulation, they're trying to pinch you on that law.
7. They actually pay attention to safety briefs.
No one cares about what is being said at the safety brief before the weekend starts — not even the person giving the safety brief. That's why it's the same stuff repeated week in, week out.
The typical CID agent probably just wants to get home to watch their copy of Jack Reacher for the 7th time this week, but they're still trying to blend in with the unit and pretend like they're not breaking any rules themselves.