Part of what the note said was "We hope you like this old card.... A small reminder of the Netherlands. It's a postcard from 1924. It was sent to someone in Rotterdam, from the Hague (46 Haag). No message, just the addresses, in pencil.
The stamp was torn, so part of the beautiful postmark was missing, but what I could see said
Great-Britain-EL or FL, looked like…
The date and town section had more numbers than a date would have, so maybe time. I couldn't read the town, and there were three stars at the bottom of the circle—six-pointed stars.
I went to the internet and started searching for information about the postmark.
I found several examples on sites selling (but not discussing) post cards and postmarks. Some showed a town, but it was not mine. Some showed the stars. Some were clearer on the long box at the right.
All were 1923 or 1924.
One town I couldn't read, two said Amsterdam, and two were clearer versions of mine: S GRAVENHAGE. If you click any of the images, you can look at them all more closely.
Most of the post marks I saw were round, or small rectangles. Those like this one were all the same and given the carious bits of clarity, it says
GREAT BRITAIN FLUSHING
It so happens that the notepaper that came with the card has a circular watermark, with three six-pointed stars on one side of the circle. Is that a symbol of something, a place, of Holland?
Why, in 1923 and 1924, were postcards from these cities stamped with anything about Great Britain?
There are stories here! If anyone comes by who could tell me, I would appreciate tales or links or clues.