Crowell & moring L.L.P.’s office faces the FBI building in Washington, D.C. Associates Jeff Greene and Jonathan Epstein knew that one of their colleagues was a big “X Files” fan, so they made a big poster that read, “Stop reading our mind” and stuck it in his window.

“He kept his blinds closed, so he never would’ve known it was there,” writes Mr. Greene, “but we got paranoid ourselves and took it down after a few hours.”