I’d say a city is well within its legal rights to remove non-city property from city-owned/controlled property.
Same thing for all the memorials to people that were killed on city streets. Noboby has a right to use public property to display personal, political or religious messages.
Let me ask......Who owns the “Public Land”? Does not the public own it? Is this man not part of the “Public”? The land does not belong to the city. It belongs to the citizens of the city.
And, anti-religious bigots have no right to demand the city remove it, either, if the city wants to continue to display it.
What's next? Are the same bullies going to demand the Liberty Bell be removed from public property because it has a Bible verse on it?