According to theater historian Cezar Del Valle, whose fascinating lecture on Brooklyn Motion Picture Theater history we were privileged to hear this evening at the Brooklyn Public Library, Park Slope's Prospect Theater played a bit part in the Cold War, when Alger Hiss was introduced to his Soviet handler in the mezzanine there.
The only evidence we have found to support this claim appears to have been authored by Mr. Del Valle himself, in a volume of essays entitled The Brooklyn Film, edited by John Manbeck and Robert Singer. Unfortunately the citation lacks a footnote:
Pete Hamill cites the same tale here. Who knows if it is really true, but it is a great story.
UPDATED: Mr. Del Valle provides evidence supporting the account in the comments section. Thank you!