The first crew member that was privy to their beginnings wasn't a crew member at all, but the ship herself. As the newly formed team got acquainted with their surroundings, it was Sara and Leonard that found themselves walking together. Leonard tried to make some small talk, but Sara wasn't exactly having it, already catching him staring at her ass once. After Sara called him out on it, Gideon was the only one who caught the look in Leonard's eyes as she walked away. If he wasn't staring at her before, he sure as hell was now.
After Sara wanted to get a drink (and weird) in the 70s, the look shared between them was a spark. Jax didn't think much of it then, (especially considering his anger about being kidnapped) but when he would look back, he would see the beginnings of their relationship as early as their first time jump. And when Sara mentioned the perfect outfit, one could see the mischief in Leonard's eyes.
But it was at the bar in St. Roch that likely changed everything. Sara surprised even herself when she asked Leonard to dance, assuming he wouldn't. He didn't seem the type. But the heat in his eyes said more to her than a dance could. She was feeling pretty playful at this point and decided if he was going to stare at her ass, she might as well make it worth his while. Mick couldn't help but grin as he watched them interact. The boss wasn't one for relationships. Hell, he wasn't much for anything fun outside of planning and robberies. But Mick saw the way Snart gawked at the blond and smiled when the boss turned to him, obviously impressed with how badass Sara was proving herself to be. He chuckled as he took another drink of his beer. These two would be fun to watch.
No one caught the irony of the line "'Cause I really love you" as Leonard smashed the beer bottles to assist Sara in their first bar brawl.
Ray, if he wasn't as depressed as he was, would have seen the look Snart gave to Sara after she convinced them that maybe they could change their fate. Perhaps just admiration for her moxie then, it certainly bloomed into much more. The drawled, "For better or for worse," gave Sara a slight shiver, but she kept it to herself for now. The fate of the world trumped the attraction she found for Captain Cold. Though, it did make her wonder about her type for the "bad ones."