Well, here we are, home at last, a day late and a dollar short--actually, an hour or two late and $250 short.
We went to a museum on the Johns Hopkins campus, and returned to see a tow truck with one car on the flatbed and our car being towed behind (the only two cars remaining on that block-length segment, the others all presumably already driven or towed away). Reaching the driver just as he was starting to move away, I got the address of where to go find the car, and them we went into a nearby church to ask for a phone book so we could call a taxi. There we learned that apparently north-bound Charles St by the campus is no-parking in the right-hand lane after maybe 3:30 to help rush-hour traffic.
While I can understand and agree with the intent of such a policy, I don't think there was enough signage to communicate it to drivers who did not already know this. I was one in a long line of parked vehicles, so I expected parking was allowed. Ahead of me was a NO STOPPING. CARS WILL BE TOWED sign with an arrow pointing to where I was not. Behind me a little bit was another sign, arrowed away from where I was, mentioning 4PM as when parking must stop. A minute of walking about before the taxi came did not produce any sign I had not already seen when I drove into the space. I must return at some future time to see if there was some sign at the beginning of this half-mile section of road about the parking regulations, although if that is the case, I personally don't consider it adequate delivery of information.
Oh, well, it was a beautiful clear 50° day, the people in the museum gift shop we had been chatting with instead of returning to the car (being unaware that it was under attack) were friendly and shared our interests. So, as with most days, it could be worse.