Simply put - A tag, or tab or some way of identifying which district a particular business is based in. Most likely response to this would be that you can RP where it is. Technically, yes, however where in-city politics want to be tested or flexed, having your own district rules on what you post in that district could really come into play, when you're in control of what goes in your district. 

Districts have their own options for setting rules, why not add that little more depth to the cities and give them their own forum identifier? 

An excellent suggestion, and I don't see any reason to not implement this.