In a METAR the wind is T, when passed to the pilot on the radio it is M. I think the references you're looking for are ICAO Annex 3 for the content of a METAR and Annex 11 and or PANS-ATM for what goes into an ATIS broadcast.
I think there is an opportunity for confusion between METARs, which technically are coded messages beyond the aerodrome, typically over the AFTN (or whatever it's called these days) and local reports which are used at the aerodrome of origination but I'm afraid I can't recall the detail and don't have the books to hand.