"What does it mean?"
"Hm? What does what mean?"
"That gesture you make with your fist clenched, and thumb extending upwards."
"Oh, you mean this?" Jim made the ‘gesture’ Spock had described.
"Yes. I do not understand its meaning."
"It’s like, um- telling someone ‘good job’, or kind of praising someone.. or agreeing with someone? I dunno how to explain it, it’s meant to be a good thing though." There was a pause, before Jim had a thought. "So.. you’ve never been given a ‘thumbs up’ before?"
"I have not."
Spock took the moment to lift his hand and mirror Jim’s earlier demonstration. It was an odd gesture, he thought to himself; and he looked at Jim, as if asking for approval of his action. Jim laughed, but he wasn’t teasing Spock. There was a hint of adoration. Spock raised an eyebrow, and before he could question Jim’s reaction-
"Awesome, you got it!" And Jim raised his own ‘thumbs up’ directed at Spock.
If Jim had noticed a tinge of green creeping up onto Spock’s ears, he didn’t mention it.