I think the city limits are stated in the laws of Vallaki? Which can be found either here on the forums or in-game near the gates of Vallaki. One of the smaller core RPs to the Vallaki scene is to get told to study the laws of the place, people should do it, or not, and face the consequences of their choice. From an IC POV I believe there wouldn't be any signs marking these borders, they would be burned for sport every other day. If people are impaired to remember that the rivers west, south, and the eastern farmlands marks the place, then sure, give them the sign... It would make more sense towards Wachter lands, which if I remember correctly doesn't have such clear geographical features to mark the limits.