Tenants' signage on property

[Renee R.]

Is it possible to disallow signage on the rental property, for example political signs supporting a candidate or an issue? I'd like to include it in my leases and head off an issue that is likely to come to a boil when the presidential election heats up. Tenants in one of my duplexes are already squabbling to the point of near violence. But, would not allowing signs be a violation of my tenants right to free speech?