Basically, it's a person bowing! The two M's are the hands of the person, the _'s are the person's eyes, and the ()'s are the sides of the person's head.
Person 1- I command you to do this!
Person 2- Yes, master. m(_ _)m
Japanese emoticon for: My apologies
M's are the hands on the ground with the the head/eyes bowing.
A: Please help me with this.
B: I am sorry for troubling you. m(_ _)m
(n) A Japanese emoticon used to convey the act of bowing to another. This usually means you admire something of them, or wish to show respect. In some cultures, bowing is also a way of greeting one another (however, if you use this emoticon to greet someone who is not from a culture of bowing, then you will most likely confuse them).
Sensei (teacher): Goodmorning, pupil.
Student: m(_ _)m
1: I just beat Halo2 in like an hour!!
2: Was this your first time playing?
2: m(_ _)m You are truly talented.