Am I supposed to meddle with homeless people? If so, how?

Walking home from the grocery store today, I saw a (presumably) homeless guy lying on the sidewalk. This was unusual because it's raining, and he was lying in a completely unsheltered area, despite the fact that there's a great big overhang on the building across the street. He was moving enough that I could tell he was alive and didn't appear to have any physical injuries, but clearly something was wrong - if he'd been in his right mind, he'd at least be across the street under the overhang.

What I'm not clear on is what I'm supposed to do. I wasn't going to approach him directly myself, because I'm a weak young woman walking around by myself (and there were fewer people in the vincinity than usual because it's raining) and he's a big, strong-looking man who's clearly not in his right mind. If he had been a clean-cut man in an Armani suit exhibiting the same behaviour, I would not have approached him directly either (although, I'll admit, I might be more likely to call 911.)

But is there someone I should call? I don't think it was a 911 emergency because he was alive and conscious and uninjured, he was just lying on the sidewalk in the rain. I don't think it was a police issue, because he wasn't doing anything illegal or threatening anyone, he was just lying on the sidewalk in the rain. I know there's a number you're supposed to call when you find homeless people during a cold alert, but is there someone you're supposed to call when you find a homeless person behaving unusually by area homeless standards during a non-emergency situation?

If he had been lying under an overhang or in tunnel, I would have just left him to his nap. If he had been lying on the sidewalk out in the open during more pleasant weather, I would have thought "Huh, that's unusual," but left him to his own devices once it was clear that he did not require medical attention. If I had found him there at night, I might have assumed that he was just sleeping for the night. But flat on his back, midafternoon, raining and not under an overhang, all makes me think there was something wrong. Thing is, I have no idea what I was supposed to do about it...