When I wan in 2nd Ranger Bn, we looked at guys with a Ranger tab, but not in Bn as Ranger qualified, not a Ranger. That was reserved for guys serving in Ranger units. Just my 2 cents.
They are entitled to call themselves Rangers although when in the Army, they would almost certainly call themselves tabbed, and more relevantly, especially after being out of the service and talking to a homeless vet, as the opening line to a conversation.