Malaysians worldwide still call Malaysia Airlines, 'MAS'.
Locally in Malaysia - 'MAS' was chosen as a colloquiol acronym (which cunningly was also short for 'Malaysian Airline System') as it emulated the word 'Emas' (pronounced - 'er-mas') which in Malay means 'Gold'. Hence MAS' previous and current service models were (and some still are) based around the word 'gold' - eg. Golden Club Class, Golden Lounge, Golden Boutique and its old inflight magazine was called 'Wings of Gold'. Its former slogan was 'Fly the Golden world of MAS' throughout much of the 70s and 80s.
Sceptics have also found other uses for the acronym however as MAS and SIA split into its current existing entities...
'MAS' - 'Mana Ada Sistem' (translates into 'Where is the System') whilst 'SIA' equally was read as 'Sistem Ini Ada' (translating into 'Here is the System').
MAS has however come a long way since the 70s and as a result Malaysians still fondly call it 'MAS'.