"The most convincing argument against time travel is the remarkable scarcity of time travellers."

"However unpleasant our age may appear to the future, surely one would expect scholars and students to visit us, if such a thing were possible at all. Though they might try to disguise themselves, accidents would be bound to happen — just as they would if we went back to Imperial Rome with cameras and tape-recorders concealed under our nylon togas. Time travelling could never be kept secret very long."

Wrote Arthur C. Clarke in 1985.

I encountered that today... doing a NYT acrostic from November 2012. The most interesting clue was: "Bill Clinton, for Nixon, or George W. Bush, for Reagan."