I've worked in psych (mostly inpatient) for almost 25 years, and I've
always used my last name on my badge. In fact, I'm v. unhappy that my current employer refused to put my last name on the badge, so I have to make do with making sure I
tell all the clients my last name every time I introduce myself.
I've been hearing about the "last name" controversy for all these years, and I just don't get it. Apart from my personal opinion that using your last name freely is the only way to conduct yourself as a responsible professional, I've never seen any suggestion that it's safer to not have it on your badge. If someone (a client or visitor/family member) really means you harm, that person is going to find a way to track you down and find you
whether or not you have your last name on the badge -- it's not like it would be hard!
Of all the things you can (and should) do to keep yourself safe, the ol' "no-last-name-on-the-badge" thing seems, to me,
very far down the list -- and yet, I always hear nurses talk about it like it's some sort of magical talisman;
as long as I don't have my last name on my badge, nothing bad can happen to me!