Mom told me she had a hobo come to the back door once when she lived in rural PA, and she gave him some food. When her Dad got home and she told him, he said "They've marked the house now. You won't be able to see where, but it's marked."
Years later I saw an article about the signs, and one of them translated as "Nice lady lives here, will give you food" and I thought yep, that's probably what got put on the house.
Another thing her Dad told her is to resist the temptation to load up a big meal for the hobo. Instead, they'd much prefer a small meal for themselves, plus a potato or onions or something similar, that they could take back to the jungle for the community pot.
Travelers are still using signs. I recently read a blog from a guy who does a lot of metal detecting in creeks and such, and he reported on a camp site he found. There was still a tent, sleeping bag and a cooler there, and a white towel hang up (which is how he spotted the site from the water), but it definitely looked abandoned. He came to find out that the white towel was a sign meaning: "Good campsite, you're welcome to my stuff."
I don't remember what the other colors for a towel/sheet/tarp/flag were, but the translations were:
- Bad campsite (bugs, bad water)
- Dangerous place (bad criminals, cops will roust you)
- Sociable, come in, have goods to trade
- Loner, stay away
Something to think about the next time you see a tarp hanging on some branches.