One interesting detail that I found, considering the presence of the Archbishop in the movie scene, is that the quote 'Be Not Afraid' is possibly a reference to Pope John Paul II's first speech when elected to the papacy in October of 1978.
My gut instinct is that it's not a prop manufactured for the film, but was simply a 'had it for five years now' possession of Bellamy's already on the desk when they came in to film for two days.
But I have no evidence to support this theory, and haven't found any matching hits looking for a vintage desk sign with that slogan.
It almost looks like a quick and dirty printed cardboard standee.
It's glossy and reflective when you see it in a moving video clip, though. Watch whenever the mayor passes in front of it.