The crossword solutions for the term SIGN ON THE PRIVY DOOR are MEN, which is a three-letter word. The phrase 'Sign on the Privy Door' is an old English saying that refers to a sign that was placed on the door of a public restroom or outhouse. This sign was used to indicate the gender of the people who were allowed to use the restroom. In this case, the sign would have said 'MEN' to indicate that only MEN were allowed to use the restroom.