lol I am one of the faker, according to the Chinese member here (The claim is ranging from floor mopping private to, actually I forgot...)
anyway, it's easy to catch these "Fake Military Personnel" A lot of them like to brag about or glorify their military service and a lot of them always talk about superficial topic and would not go deep down into service (Not talking about classified stuff) They talk a lot about some easy/simple thing (like Rank structure or Regimental/Brigade information) and those people will go after other and correct them, vet or no vet, when these people started to misquote or make mistake on some tiny things (such as addressing Sergeant/NCO as Sir and so on) When actual service member don't really care about when we are civvies.
Most of these people get caught quite easy, and I have met one of these "Faker" on another forum, who claimed to be (or was ) a US Marine living in Australia, with Darwin having been hosting a Marine Regiment, it would not be that suspicious, but when he start talking, you know he is a faker. He got exposed for not knowing what is CAC.
The hardest to catch is those who actually serve but ballooned their service, that you will need to know one's service record, although it can be search in various mean but mostly people don't really dig that deep unless that's your job (like CID or some group that aimed to catch these people)
In reality, military service are seldom talked about within the Military Circle, one reason is military service is not anything that glorious, especially when you have to endure hardship to get to that level, you would want to forget instead of keep talking about it and keep reminding yourself on it. Two. The Military Experience is almost the same across a whole wide range of ex-servicemen, what the other go thru I have went thru, and what I went thru the other could have, and if you talk to a person who never serve before, they won't understand and thus, you won't talk to people who did not serve about it, and you would not talk to people who served about it, in short, you don't tell anyone nothing.
There are service laws, at least in Indian sub-continent, that
do not permit public discussion/discourse by active service personnel and the same is enforced quite strictly, for if discovered, the repercussions are quite severe.
However, few are active on this forum itself, and like
@Oscar mentioned, those masquerading as one, get caught quite quickly.
unless you are talking about Classified stuff, everything is open within the US military. Not too much classified stuff to begin with actually, and classified stuff also do have a time stamp on it, so it's status would expire as time goes by.
I can send you a field manual on Counter-Intelligence technique over the internet, and you can actually train as one by one of the US military authorised trainer, but you won't get trade secret like tradecraft and station code online, those are classified.