Maybe not true everywhere but in all the towns I have lived in the homeless were well aware of organizations that provide assistance. No need to carry a card about it.

Indeed, and there's usually a reason why they're on the street instead of going to those organizations (justifiable to a random other person or not).

My experience is they are already using those services but most of those services can only provide so much. In my state most people on the street already have Medicaid and food stamps but it isn’t like that is enough to get you a place to live or a job. The programs and services available can keep someone alive but are rarely comprehensive enough to deal with chronic mental and physical health issues that impact the ability of someone to thrive in a market economy. Even the most rightwing 20th century economist recognized that the state will need to step in for housing and employment for some part of the population.