Was just up in Tacoma/Seattle last Friday and ended up doing a Sound Transit day - Tacoma Link, Sounder to Seattle, Central Link to Sea-Tac and ST Express Bus back to Tacoma. All four modes.

Took PLENTY of photos. In plain view of security guards. Nobody even approached me, much less said a word.

A couple years ago I was in Tacoma at Freighthouse Square (on a weekend, so there was a parked train but no operations) and I took some pictures. A security guard out of nowhere started walking towards me, saw I was causing no problems and then walked another direction. Never said a word or anything.

I agree, King Street Station's platform is probably not advisable - too many people, no space. You can get some O.K. shots from Jackson Avenue or the pedestrian overpass.