"Danger! Look out for bees! Don't shake trees!"
— Signpost, City Folk
In Animal Crossing
In Animal Forest, Animal Forest +, Animal Crossing, and Animal Forest e+, signposts will have hints written on them. Some hints are written by Tom Nook, some are written by Redd. They are not to be confused with Sign Boards. Signposts mark where villagers' homes may appear (except the one from Kapp'n near the dock). If a villager moves out of town, a signpost will appear where their house was. When a villager moves in, their house will appear where a sign post was. As such, the player won't be able to plant trees too close to a signpost, since that space is reserved for new villagers' homes.
In Wild World and City Folk
Signposts serve the same purpose in Wild World and City Folk as they did in the previous installments, though sign boards do not reappear. Some signposts are written by Tom Nook, some by Redd ,some by Pelly or Phyllis, and some by villagers or other special characters. When a new villager moves in, they move on top of one of these posts.
In New Leaf'
Sign Posts reserve spaces for villagers to move in. They are written by Tom Nook the day before they move in. A fence will surround the space for the villager's house. They say: "This spot is reserved for ___ 's new home. Nook's Homes.