In the opening scene of MIB (the first film), K and D arrive when a border protection agency are stopping refugees from being smuggled into the country. K explains they are from Division 6, to which the border official responds there was no such thing. The MIB also take substantial methods to erase the identity of their agents and protect the secrecy of their existence. K also explains to J that they are a self-funded agency. My question is, are there any humans who are aware of the existence of Division 6/the Men in Black operation (as the aliens on Earth obviously know about them)? I am willing to accept answers from the original comic book series, the films (although I don't recall any evidence that suggests any humans were aware of the MIB) and the animated series.
There seem to be 2 questions in one here:
Do any humans know about Division 6 (the Men in Black)
Answer: No - because "Division 6" isn't Men in Black, it's INS and doesn't exist.
It is a made-up government branch that Agent Kay told, to give official sounding credentials to the border agents (who are part of INS).
Whether the IDs they had were actually made out to be "INS Division 6", or he made up the name on the spot, is not known (and an interesting side question).
From MIB script:
KAY: We'll take it from here.
AGENT JANUS: Who the hell are you?
Kay and Dee flash some form of ID.
KAY: INS Division 6.
AGENT JANUS: Division 6? I never heard of Division 6.
AGENT JANUS: You ever heard of Division 6?
2ND INS AGENT: There is no Division 6.
3RD INS AGENT: Who are those guys?
Do any humans know about MIB? (who don't work there)
in "MiB", there are clear indications that none do, and it's a matter of policy to flashy-thingy everyone who's not in MIB but learns of them:
Of course the border patrol agents
Kay neuralizes Jay after going to Jeeb's place
All agents are memory-wiped when leaving the agency (Kay flashed Dee at start of MIB; and Kay himself was flashed at the end of MIB).
Kay wants to flashy-thing Laurel Weaver repeatedly
Jay neuralizes everyone in MIB2 (his partner, presumably so many previous partners that MIB workers are afraid of him neuralizing them for a minor infraction)
Even more importantly, in MiB2, Kay clearly says it's a matter of policy, and Jay effed up when he didn't neuralize the witness Laura:
JAY: I'll contact the witness. We'll talk to her.
KAY: Things have changed. We used to neuralyze witnesses.
JAY: See, originally, I'd... No, I was going to... I interrogated her.
KAY: Then neuralyzed her?
KAY: MiB code 773/I clearly states that all civilian personnel...
I saw DVK also posted a similar question regarding Division - 6 and its usage in MIB - verse.
It is a running gag that is observed in not only the MIB movie, but also in MIB animated series.
In the movie KAY poses as INS Division 6 agents. During the animated series there are references to United Nations Security - Division 6 and Fire Marshal - Division 6 as well, as an excuse for covering up.
So your first questions's answer - NO, there is no Division 6 of INS or UN Security or Fire Marshal. These are all coverups. And Secondly also - NO, the ordinary humans do not know of MIB or its operations because of the MIB directive 773/1 as quoted by DVK.
.. .. .. And flash.. A Blue Light.. And You forget everything.. Real handy tech.
Another piece of evidence indicating that Division Six is indeed a made-up cover is the lyrics from Will Smith's rap Men in Black:
Walk in shadow, move in silence
Guard against extra-terrestrial violence
But yo we ain't on no government list
We straight don't exist, no names and no fingerprints ...
Not exactly the best piece of evidence, but it is sort of in the movie (it's played at the end with the credits)
Definitely yes. We saw in Men In Black II that a cheesy TV series was made which showcased some of their previous operations. While the effects were unrealistic in-universe, and some details were wrong, MIB is explicitly called out by name, and one of their encounters is described in detail. Since this is an episodic series, it's probable that there was more than one such installment. So there are definitely some non-MIB humans who know about MIB.
Furthermore, we know the neuralizer is not perfect. It's reversible. Additionally, in large cases, like the one where they use the statue of liberty, or a single neuralizer on large crowds, someone might not see it. People blink randomly, and someone might blink long enough to ignore it. Someone has almost certainly slipped through the cracks at some point, and we know they remembered enough details to make cheesy television.