There isn't a prime directive. I go with the flow. Most of the time I learn that others are autistic or ND or might be autistic or ND when I share that I am autistic. Also, it depends on our relationship. I saw somebody two nights ago who looked like they were stimming, but I said nothing. They were the merest of acquaintances.
Conversely, I asked a girl I went on a date with whether she was ND, and she said she thinks she is, given that she was on a date with an autistic enby (me) and her girlfriends are all autistic.
Context drives what I do, but there is no prime directive. Do be prepared for backlash if you speak out of turn, however. I've not encountered the backlash, but I suppose it exists.