Thumbs up convey the message of power, dominance, and superiority.
Hands in the pockets with thumbs protruding up give the impression of a confident and authoritative person. Also, this posture gives you a relaxed appearance that translates confidence and self-esteem.
Women use this posture usually when they are posing for a shot while men often do when they want to look cool and show their superiority or want to impress a woman whom they feel attracted to and get her attention.
One hand in pocket with the thumb sticking out is a high confidence display and comfort.
It’s a resting position especially when you lean against a rail or support your back on a wall. You often find this posture in fashion magazines or on the runway when models hold a jacket over one shoulder showing a nonchalant elegance with a striking pose.
Read more about other postures here.