Where did this happen, and why did you comply? I would politely remind any overzealous/power-tripping/paranoid railroad employee, security guard, or law enforcement personnel of the following:

1) There is no law that prohibits photography of anyone or anything from public places. Previous attempts by transportation agencies to restrict photography were rescinded due to legal threats.

2) There is already a prolific body of photographic work about Amtrak and transportation in general available online, in books, etc. Taking more photos poses zero security risk.

3) Railfans and photographers are the top civilian eyes and ears out in the field. They know better than anyone if and when something is wrong. They should be embraced, not attacked.

4) Amtrak employees should especially know better. For the past four years, the official Amtrak calendar has featured photos submitted by railfans as part of Amtrak's Picture Our Train Photo Contest. If Amtrak is actively soliciting photos of their trains, it's an even greater embarassment for their employees to be attacking photographers and their rights.