John Sheppard and Nikita Mears
There were probably a lot of people, not just her, that could tell he was former military. Though, technically he was still part of the military. If they ever went back home he would still be part of the Atlantis team. That was something that would never stop. Same with Ronon and Carson. They'd always be a part of the Atlantis team.
"Yeah, first timer with this," he tells her with a smile of his own. "Someone sign you up before?" After all, she did just mention that this was the first time that she'd signed herself up. "Hey, I mean it's a potential to make friends more than anything else."