You'll probably get more responses in the Amtrak forum, but here goes.

Amtrak's identification policy can be found here:
http://www.amtrak.com/servlet/Conten...Page&c=am2Copy

Amtrak requires you to show your photo id if you pickup or purchase tickets from an agent. On board trains, you may be asked for an ID. The conductors conduct periodic random ID checks, usually picking a number from 0-9 and then asking for ID for all tickets that end in that number