Respectful is something that's immediately apparent in the first conversation you have. Doesn't talk down to you, doesn't talk over you, takes you seriously, doesn't dismiss your opinions or tastes. Even if you disagree it's a disagreement of equals. An easy example - I'm mixed-race and there have been several issues around race that DP, as a white man, had never thought about before. I'm used to white people, even well-intentioned ones, sometimes reacting defensively - he didn't, even when he didn't quite get it immediately and had to process new ideas.
Kind is less immediate because to me kindness to me involves knowing me very well, and specifically knowing my weaknesses and the things that make me frustrated or anxious. And then supporting, reassuring, giving me the grace to be kind to myself.
But I would say that someone's kindness to other people can be evident from the off. The old litmus test of how they behave to waiting staff, cleaners, bus drivers, of course; how they talk about people generally (no unthinking snobbery, classism, racism, misogyny, homophobia etc); how they behave among people they know (a month after we met, DP went round to his friend's house to batch cook two weeks' worth of food for her as she'd just given birth). Look at how they make other people feel, not just how they make you feel.