There's a few interesting examples of hobo sign at Willa's Journal. For example, the one on the right apparently means that a "kind-hearted woman lives here." There's also sign for man-with-gun lives here, and you-can-sleep-in-hayloft. Interesting to compare the vocabulary with Lapine, the imagined world-view of rabbits. Wikipedia has a little bit more information, and there's a good "alphabet" at slackaction. Although there are plenty of alternatives.