Leaving notes is nice, but a sign that can read easily by a player on the screen for our front yards would be nice (similar look to the signs you see in public gardens).
Also, traffic style signs. They might be based on furniture. Heck, they might be furniture. But they'd have glyphs on them that you could choose from, for faster communication. Mostly, I think these would end up being ignored, but I think they'd look cool. So maybe they should be mostly silly. Like a gnome crossing sign.
edit: I should point out that this is in addition to Humbabella's request.