As a Jewish person, this is a tough situation.

The City can't really legally restrict speech, no matter how offensive it may be. This is especially true for "political speech". The statement that The City made to Wish TV is correct.

The City can address zoning violations and/or hazards that may make the property a blight or nuisance. It wouldn't address flags or written messages.

If The City gets the guy to clean up his property, it would only showcase the flags more and make it less likely that people dismiss his flags as crazy. If The City fines him for zoning violations to the point of foreclosure, it'll almost certainly feed into antisemitic conspiracy theories (and potentially open the city up for a civil rights violation lawsuit if they haven't been applying the zoning laws equally).

Maybe it's best to not give this guy attention and wait for him to die quietly.