This is a difficult situation. There is a "rule" in UE (as much as there are actually rules in UE) that one doesn't explore individuals' homes. This is common sense -- would you want someone coming into your house and exploring, even if they didn't do anything except take pictures? However, this rule gets iffy when it comes to the homeless because one doesn't necessarily expect an abandoned warehouse/subway/mine/theater/etc. to have occupants.
I'm not sure that there is a "usual" policy for dealing with homeless people, any more than there is for dealing with security guards -- it's more a series of guidelines, and not all of them are UE-related.
I'm with you, Fiddler -- I have been conditioned never to give money to the homeless. I feel badly for them, certainly, but a big percentage of them have substance abuse problems and I wouldn't want to be supporting the thing that is keeping someone from getting help. And although it seems like it would be common sense, I am conflicted about giving indirect help like giving or buying clothes. It seems like it would be a great idea, but you never know whether they'd be able to trade/sell that brand new jacket to other homeless individuals for drugs/drink. It's a more remote possibility, though, so I would feel more comfortable doing that than giving money.
The best thing to do, I think, would be to give these people the tools to help themselves. For example, instead of giving money, give them a card telling them where all the local shelters/food pantries/clothes banks are. And then give money to the shelter, or volunteer your time there.
Of course, that's more of a cerebral thing (a feeling that, "I've done my part") which doesn't really help when you pass someone on the street and s/he is shivering in the winter cold. But unfortunately homelessness is one of those problems that can't really be solved by applying logic from one's own life. After all, you think, "if I were living on the streets, I would want someone to help me out by giving me a coat, some money, etc." However, more often than not, it is something pretty unfortunate that will drive people out onto the streets -- familial abuse, substance abuse, mental illness, etc. And these are problems which the average person walking by on the street can't really help a whole lot with.
So, in my eyes, it's a matter of making sure you've done what you can in a way that won't exacerbate the problem and then treat individuals on a case-by-case basis, mostly by referring them to specific services where they can get help themselves. The unfortunate thing is that you can't ever MAKE someone want to get help. You can only point them in the right direction, and then they need to help themselves.
How's that for some dime-store psychology/sociology?