Non-Manual Markers:

Hearing people use vocal inflection to convey the meaning of something they say. How would you say the following sentences? (Listen to your voice.)

Hi, my name is…
How are you today?
I am so excited to meet you!

Nonmanual markers consist of the various facial expressions, head tilting, shoulder raising, mouthing, and similar signals that we add to our hand signs to create meaning, much in the same way vocal inflection does for spoken languages.
The sign for nonmanual markers is to fingerspell "NMM."
Much of the meaning in ASL is conveyed via non-manual markers. It's more important to show the meaning on your face than what you are signing with your hands.

Some common non-manual markers:
Wh-Question: eyebrows down, head tilt, body tilt forward

Yes/No-Question: eyebrows up, head tilt, body forward

Good mood: smile, body relaxed (open)

Bad mood: frown or little facial expression, body stiff (closed off)

Angry: frown, body stiff, "puffed up"