5301991f_and_The_Art_of_Breaking_Things__detailed_explanation
[signal] Pursing lips [part of body] mouth [possible meaning(s)] thoughtfulness, or upset [detailed explanation] 
As if holding the words in the mouth until they are ready to be released. Can also indicate anxiousness or impatience at not being able to speak. Or quite differently can indicate upset, as if suppressing crying.
“I pretty much try to stay in a constant state of confusion just because of the expression it leaves on my face.” – Johnny Depp | Zen and The Art of Breaking Things
detailed explanation