Question: are they saying mom in bodyguard?
Answer: Richard Madden's character David Budd is referring to Julia Montague as Ma'am as you correctly surmised but he is saying M'm that sounds like Mum which is a contracted way of saying Ma'am. ... Mum is short for Mummy, meaning Mother. In The Bodyguard they are saying 'Ma'am', short for 'Madam'.