Real pot smokers can spot their ilk during a social situation with little, if any effort. It might be their relaxed swagger or their slow, careful delivery of speech. Or the dim innuendos that hint of their forbidden pastime.
If all else fails, the more boisterous proponents of herb will make blatant references or just come right out and offer it to you... if you're lucky. (Be warned. Some of these shit talkers are nothing but, merely fishing to find out who else is carrying.)
Regardless, we tend to find each other quickly and often. Smokers cluster and multiply faster than a computer virus in a Microsoft application. You'll see a couple of guys meet, chat a bit, get to know each other's hobbies.
"Oh, you kayak? Me too. We're taking a trip to the American next month." And so on.
Then they're off. One goes to get his girlfriend, who grabs a friend. In a few moments, six or seven ladies and gents are huddled around the corner of a house in a perfectly good neighborhood, passing a stiff joint and talking like they've known each other for years.
And this kinship is justified. There really is no better way to get to know someone than to commit a crime with them.