Thanks to Roger for setting our weekly challenge today.
Image : https://morguefile.com/creative/GaborfromHungary/4/all 3bd328e827ad878ce609dad27ac2c21a
The disused building was their secret place.
If a message was left through the makeshift letter box, a mark was made on the wall outside and when retrieved, rubbed away.
Each had their own special mark, so there was no chance of a message being missed or sign ignored. Rendezvous could be arranged and it worked well for everyone.
This arrangement was in place for twenty years. The last mark was still just visible and the unopened letter stood on its edge at the bottom of the drop where it had fallen before the final bomb dropped.