When I was on my bicycle tour in Central America I used an app called iOverlander and used it when no WS hosts where around. The iOverlander has a symbol of some street signs and I noticed at a few places I stayed at, even in the towns, people marked their driveway with the same symbol, red square with the white sign symbol, you can look it up by going to iOverlander.com. I think the symbol changed actually, I can't remember what it was before.
Anyway, I was thinking of taking a old child's bicycle tire and paint it the same greenish-blue color the WS site has and bolting it to my fence post. That way 99.9% of people that see it won't think anything of it but people who do WS would recognize it.
Is there any other symbol I could use to alert bicyclists they have a place to stay here? I live along the highway and see people go by occasionally.