Tenants don't like other tenant's outdoor flag - what to do?

[Jessica Todd]

Hi all -- In my 4-plex, I have a tenant with 2 large flags draped over his 2nd floor balcony -- both very clearly express his viewpoints on certain topics. I have received 2 complaints regarding one of the flags; they feel the large size make it seem his viewpoints represent the entire building.  While they don't bother me, I want all my tenants to feel comfortable in their home. I don't have anything expressly written in my lease against this and I worry if I ask him to remove one or both, it will be a violation of the tenant's freedom of speech.  Any recommendations?