Because of the period of hyperinflation, one day I had a boss unwittingly hand me $500. She bent down and said, "Ooh! Someone dropped a quarter! Wait this ain't a quarter, what the heck is this?" She then handed me a 1934 500 Deutchmark coin. I told her what it was, and asked her if she wanted it. She said she wouldn't know what to do with it, so after I sold it, I gave her $75 as a 15% finders fee.
The only foreign coin I have came from a roll of quarters I got in 2015. Back when I visited the laundromat weekly. I stuck my quarters in the machine, but this one kept getting spit out so I checked it. I didn't recognize the characters on it, but I had an Iranian coworker who might so I took it to work and asked if she knew what it was. She immediately goes, "Oh! This is a dirham! It's from the UAE."
One thing I forgot to mention, the thing that gave it away was it was cast out of aluminum, so it was really light. Probably worth a lot more these days, since this was about 16 years ago