You have observed the diamond shaped signs on rail cars. You may understand that they are there to warn of the possible hazards of the materials in that rail car. What you probably want to know is what are the correct markings or signs should be on the rail cars on my layout. With this clinic I will share with you a little history of the warning signs, now known as placards on railroad equipment. We will see what the correct placards are for what commodity in which era. We will start with the 1906 American Railway Association Regulations for the Transportation of Inflammable Articles and Acids and review the changes up to the current DOT regulations