AT&T MERLIN LEGEND Release 2.0 Analog Direct-Line Console Operator's Manual page 77

Features
To Program an Extension Status Button
1. Label the buttons to be programmed as follows:
NOTE:
The labels suggested refer to the Extension Status
feature used by businesses with housekeeping or
health care services.
2. Slide the T/P switch to the P position.
3. Press one of the buttons to be programmed.
4-28 Extension Status
ES Off
ES1
ES2
ES Off means that the light next to that
extension is off. (Room is occupied and
telephone is in regular call-handling status.)
ES1 means that the light next to that
extension is flashing. (Room is unoccupied
and ready for cleaning; outside calls cannot
be made from the telephone.)
ES2 means that the light next to that
extension is on. (Room is vacant and
outside calls cannot be made from the
telephone.)