Part of what makes the Tower of Terror so great is it tells a story and throughout the attraction, you will find references to what happened on that fateful night when the Hollywood Tower Hotel became a Tower of Terror. These visual clues are included in the attraction by Disney Imagineers to give you a hint that something very bad happened on October 31, 1939.
This menu from the Sunset Room (located after the ride near the gift shop) lists the last menu that the hotel was in operation for, October 31, 1939. Imagineers wanted the hotel frozen in time so they included everything they could to show you that since the incident, everything has been left in tact and basically once everyone left the hotel, no one has come back to touch anything.
This reference to this fateful date is a little bit creepier. You will notice that the elevator permit is signed on October 31, 1939 which is creepy enough considering the elevator permit was signed the same day the elevators were the scene of the incident but the signer is Cadwallader, which in a Twilight Zone episode is revealled to be the devil.
Finally, we have this note which is on the counter in the lobby of the Tower of Terror which reads "Reservations for Oct 31 - Arrival delayed". The note is for a Mrs. Adams who is to arrive at the hotel the day of the incident and likely it's for dinner, which would be about the time the incident occured.