Santa Fe used both numbers and letters to identify their trains. See attached link.
http://www.qstation.org/ATSF_Train_Symbols/#:~:text=ATSF%20Numbered%20Trainshave%20the%20following%20format%20%23-%23%23%23-%23%23%20and,the%20hottest%20and%20a%201%20being%20the%20slowest.
BNSF uses letter...