Good job Soapy. I don't know how many license plate #s I have written down, when something just didn't look right. I've been asked why I did it when they weren't doing anything wrong, often being scrutinized as if I was doing something wrong. I explain that if I'm wondering what they are up to, they may have had sinister actions in mind had I not been there, and if I find that something bad happened during the night I would instruct the police to look at them first. Nothing happens, no harm, no foul. I always get quite irritated when I hear someone say "I wondered what he was up to..." and when asked for the tag # I hear "I didn't get it."...
On a side note, I was at the c-store down the street, when an attractive, nicely dressed, woman was wanting to cash a check. She instructed the clerk that she was related to the "Johnsons", a very prominent family in that small town. Also, that would be a very prominent name in the phone book at any pay phone (this was a while back). From where I was standing, I could see her car with Illinois plates (nearly 200 miles away at closest point), and memorized the # until I could write it down. The clerk refused to cash the check and they left. Lo and behold, a few days later I read in the local paper of a bunch of cold checks being passed, and fitting the description of the woman and car. I still had the # written on something in my truck and passed it along to law enforcement. I never heard how it turned out.