FOS

From SA Mafia Wiki

An FOS, or Finger Of Suspicion, it used when a player finds another player just suspicious enough to point out, but not suspicious enough to warrant a vote. It can also be used when there are two players who you find equally suspicious so that you can vote for one and place an FOS on the other. They are most often used around endgame, when an errant vote can easily be piled on by the scum and get an innocent player lynched.

FOS is not a very commonly used acronym in forums games