Maybe my approach is different. I just say something along the lines of "Hi, I don't think we've met." and go from there.I've been in plenty of classes as a student where there was a person there I'd never trained with, so to them I was a high-ranking student they'd not met (and might not readily recognize). Within NGA, belt rank typically tells you what techniques they are capable of taking the falls from, among other things. So being able to identify the new person wearing a rank as not part of the school's regular group (rather than just a person of that rank I'd not met) is helpful.