Hope I'm not too off-topic as this is the Railroad/Raifan forum...
Anyway, I've been photographing emergency vehicles for years and have been detained off-and-on by law enforcement and security personnel. What's more startling is when a "Concerned Citizen" approaches and asks what I'm doing and why! After 11 September, the photography hobby is definitely more difficult and I can understand it up to a point, but it seems that common sense is out the window.
Regardless, I usually just stop in at a local PD/FD, toss 'em my driver's license and "Hobby" business card with contact info, and ask if I can get some photos. This works well, but on the street or near the tracks, what are you supposed to do? Search for a person in authority or wait until one gets there after you've lost your chance to get a good picture?
I'm contemplating getting a pair of those new digital camera binoculars at a popular radio and communications specialty-store, but they only have two megabytes of internal memory! I can only just imagine been seen and reported for suspiciously "Scoping" something out. Again, I understand and respect the concerns of police and others, but until Google Earth gives me the option to zoom down from my home PC to capture some good photos, there has to be an easier way.
By the way, I visited Port Columbus International Airport (Columbus, OH) last summer with camera in hand and stumbled onto a few nice and shiny cruisers parked in their fleet lot. I found and approached a police officer, gave him my license and card, and asked if I could take a few photos. He walked away, got on his cell phone, came back literally two or three minutes later and said, "No. Do you have any other questions?" Not more than two weeks later, that story about the UK trans-atlantic airline plot hit the news. Go figure. No patronization intended, but I guess I'll give Port Columbus Police an "A" for the day.