RATS

The Radiation Trefoil System, or R.A.T.S., is a special indication in the Fallout Official Survival Guide to warn the readers when a chapter might give away more information than the readers want, to prevent for learn too much about the game and destroy the suspense.

Characteristics
The system is divided into a bar with four rats inside. There are 4 levels, the 1st level have no information outside the chapter and the suspense, to 4th level with a wealth of information on the content of the game, each described with a humorous sentence.