I met Sylvie for the first time (and probably the last) this past Tuesday. It was a bitter cold morning. I spotted her jumping on the car in front of mine on the road between my village and the next. The car slowed and then drove off. I stopped because this smallish lab-pit cross looked desperate. She circled my car, checking out the doors. I opened the front door, she jumped across my lap and into the back seat. She promptly hopped back into the passenger seat, licked my face and then hopped back in the back seat, curled into a tight little dog ball and went to sleep. This was obviously an experienced car dog. When I got to my office I called the vet on the rabies tags and got the name of an owner. The owner it turned out was in the hospital with a infected surgical wound. His voice conveyed how much he loved his canine companion. To make a long story short between the two of us we located a friend of his to care for the dog until this man could be released from the hospital. Sylvie it turns out is an escape artist. In this case she managed to sneak out when her caretaker came to visit. Her little paws were abraded and bleeding but it was an easy clean-up and fix.
I have repeated this scene dozens of times over the years - all but once I've picked up the animal and found the owner or someone to care for the it until the dog or cat's human could be found. the one time I fail to do this little kindness and have for 20 years regretted the decision.
If an animal is behaving strangely or is aggressive leave it alone and call the police or animal control. But often one can help. Sylvie was a delight. She was a perfect guest in my office - better than my two canine companions (embarrassing but true). Worth the little bit of effort!