I find that writing little notes to students on scraps of paper is one of the best ways to create an inviting, caring atmosphere in a classroom. None of them are super, super serious in content. Most, in fact, just say something like, "Hey, that logo you designed yesterday was pretty sweet." And then I add suggestions for revision if I want--but that usually doesn't happen.
Other times, when a student isn't acting/responding normally, I'll give them a short note that says something to the effect of, "Hey, you seem a little off today. Hope whatever it is improves soon."
These two types of notes, generally sorted into "You're awesome" types and "Are you ok?" types, make a huge difference in classroom community. I see them stuck into binder covers, and former students tell me they keep them for years.
It just goes back to my bedrock thesis of education: treat students like they are people, because, you know, they are people. Notes that just say, "Dude, I see you, your humanity, and your value" carry huge, huge amounts of weight in building the kind of environment we enjoy and can learn in.