There’s an interesting story about the Soviet defector that had a code like this where he was to walk down the street at a certain time holding a Safeway grocery bag (apparently this was not unusual even in Moscow to shop with an old American plastic bag), and he actually had to use this option and was subsequently exfiltrated from Russia.

https://en.wikipedia.org/wiki/Oleg_Gordievsky See the Escape From the USSR section under Career