Not sure where I first found this link, but:
"Hey, listen. I'm a veteran. This is a V.A. facility. I'm sitting here not talking to anybody, having a cup of coffee. I'm not protesting and you can't kick me out.""You'll either go or we'll arrest you," Adkins threatened.
Smacks of the whole "Free Speech Zone" BS.

i wonder what the shirt *said*
Well, he said it was a "Veterans for Peace" shirt. Some more information is here (including an interview with Mike Ferner) So I'm assuming it was a standard VFP shirt like these.
He didn't actually say what shirt it was in that first article at all, other thant he article title, unless I missed it... that second one has it, though.