Join Date: Oct 2006
Location: IAD, and sometimes OMNI/PR. Currently: not far from IAD, but home will always be SAN (not far from the "touch my junk and I'll have you arrested" Memorial TSA Check Point) even if I'm not there so much these days.
Programs: UA, CO, Calcifer Award for Mad Haiku Skillz
Posts: 5,076
My experience is that, if given a choice, their preferred tip would be cash. YMMV. I'd put it in an appropriate holiday-themed card with a note of thanks and a signature.
I wonder if there are any concierges/former concierges in our midst who would care to comment on this.