Hobo?
Dating back the 1930s at least. Still in use.
Hobo Signs
Hobo Signs were originally created in the 30’s so that people ridin the rails could communicate. Over the years some people have stopped using them, but you can still find them if you look. The best places to find these are on the exit ramps of small towns scratched into the post, outside of abandoned buildings, squat houses, and occasionally you will find them outside churches. Especially the ones with kitchens. Every know and then you will see these symbols written on the mailboxes or houses in really small towns located next to the railway. These symbols will vary slightly from place to place, and from artist to artist. If you know the basic symbols they are pretty easy to translate no matter where you are. Most of these symbols can still be found all across the U.S. and some of them are used in Europe as well.
http://www.vagabond101.com/hobo-signs.html