When the S shows through the safety selector, the safety is "on", meaning the gun should not fire.
When the selector is pushed forward to the "off" position, the gun should fire. When the action is opened, the safety will automatically reset to S or the "on" safe position.
If the safety selector is pushed to the rear, the safety is off and so is the automatic reset. In other words, the gun will not go back on safe when the action is opened. The triggers will be ready to fire as soon as the action is closed without any manipulation of the safety. This position requires the user to push the safety forward to the S position to get the gun back on safe.