Originally Posted by
gulliBell
An (M) symbol in column 4 of the MMEL/MEL indicates that a specific maintenance procedure must be accomplished before beginning operation with the listed item of equipment inoperative. The aircraft mechanic will do what the MEL says to do and an appropriate endorsement will be made on the aircraft maintenance release.
Exactly - hence my comments. E.g from my link:
2140-01
Cabin Heating
System
C
1
0
(M) May be inoperative provided the valve is secured to the "OFF" position.