A question about The Watchmen (movie)

TV Tropes on “Zeppelins From Another World,” a sure sign that you’ve slipped into an alternative universe such as President Nixon’s fifth term: http://tvtropes.org/pmwiki/pmwiki.php/Main/ZeppelinsFromAnotherWorld

I don’t remember any of the airships in either the graphic novel or the movie being clearly identified as police.