In the US, pretty much the only time you’d see people walking down the street holding hands is if it’s a couple being romantic or a parent walking with a small child. We don’t do a lot of hand holding outside of romantic partnerships (although we’re very big on hugging hello and goodbye, even with people we don’t know particularly well).
This is absolutely not the case here. Although Austrians are typically more socially reserved and formal — especially with new people — it is much more common for them to participate in more public physical contact with people they know well (enthusiastic public kissing is as common here among middle-aged adults as it is between teenagers). Specifically, I’ve noticed that it’s quite common for friends or family to hold hands or walk with their arms linked here. You see it most commonly with women and their female friends, as well as with mothers and daughters.
It seems very nice — relaxed and warm and intimate. I think I’m noticing it in particular lately because I’ve been missing home, and my family and friends, lately in particular. It just seems like a nice way to be connected to the person you’re out with — not two people walking near each other but two people walking together. It’s just a simple little thing, but one of the many that I’ve seen here and thought, “That’s nice — why don’t we do that?”