I was not at that event, so I did not see what Drew saw. However, in the past, I have been approached on two occasions, once at Loma Linda and once at Tehachapi XO. Both times trespassing. The Loma Linda event did not start out well, probably because I made an illegal U-turn in a grade crossing, immediately entering UP property. In typical Johnson Luck, the Special Agent had just pulled out onto the street behind me as I made my move. Careful diplomacy on my part cooled his hot exhaust. As far as his physical appearance is concerned, as he was approaching retirement age, he did not seem like he would be able to chase me far if he had to. But, his SUV was neat and orderly, (I was fortunate enough to not have to make an up close and personal inspection of the back seat) and his uniform presentable, complete with shined boots.
The second occasion occured at Tehachapi XO well after the UP installed all the No Trespassing signs. That event was even less remarkable, and I enjoyed a ten minute conversation, after he carefully explained his position and ensured I knew I was not considered welcome near a potentially hazardous environment. He also waited nearby until after I got my shots and left. His physical appearence was also in-line.
Granted, it probably helps that I work as a rail, but I don't mention that unless it comes up.
Where I work, private security patrols the yards, and contacts the Special Agent or local fuzz, depending on the circumstance. Most calls revolve around three usual happenings: Taggers and trespassers, doors open on containers and riders.
Personally, I support the idea of armed response with federal powers. As a craft employee, I travel through some crappy parts of town, some very remote locations where container break-ins by organized gangs and I am usually by myself, unarmed, walking and far from any sort of reasonable protection should I be accosted. I'd like to see more Special Agents, along with -and I feel this is important- a better attitude towards railfans due to thier high interest and usually very accurate knowledge of "what's happening and where". More eyes and ears out there can only help.