I guess this amounts to a chicken-and-egg problem. In many European countries, police officers are only minimally armed (just a handgun, used only in rare circumstances).
And yet when I've been in Europe I've seen plenty of police and/or paramilitary units carrying submachine guns, something I never saw here in the U.S. even after 11 September.
Conversely if you want to see the use of the AR-15 in public artwork, you should go to Northern Ireland.
In Switzerland I once saw a conscript get on a train and put his rifle in the luggage rack exactly as if it were an umbrella. But Switzerland is different (guns are mandatory, ammunition heavily controlled, the people are the "militia" and support the government, and the whole country is a mountain fortress).
They were there, mainly at the airport. Not in recent years, and probably not very long after 2001, but I certainly saw armed military at the U. S. airports for six months or more after 09/11/01.