English: Composite photograph showing the location of the train numbers (highlighted in red) for each possible Caltrain location. Train numbers appear on the leading element of each train consist. Since northbound trains are led by a control car, and southbound trains are led by a locomotive, with two of each type (locomotive and control car) there are four possible locations for train numbers. Cropped and resized from the sources listed.

• Top left: Train number location on MPI Caltrain locomotive
• Top right: Train number location on EMD Caltrain locomotive
• Bottom left: Train number location on Bombardier Caltrain control car
• Bottom right: Train number location on Nippon Sharyo Caltrain control car

Each train is assigned a three-digit number indicating direction, sequence and stop pattern. This number is not to be confused with the locomotive number, which is the 9xx number physically stenciled on each engine. Only the MPI locomotives display all three digits; all others (EMD locomotives and control cars) display the last two digits only.

• The first digit for weekday trains is always 1, 2 or 3, indicating stopping pattern. 1xx trains are local trains making all regular stops. 2xx trains are limited-service trains, skipping some stations. 3xx trains are Baby Bullet trains, and make the fewest stops.^[1]
• The first digit for weekend trains is always 4 or 8, also indicating stopping pattern. 4xx trains are local trains making all stops. 8xx trains are Weekend Baby Bullet trains, making fewer stops.^[2]
• The second and third digits indicate the sequence number of the train. For instance, x01 is the first train of the day. These digits also indicate the direction of the train; odd-numbered trains run northbound, and even-numbered trains run southbound. Thus x02 is the first southbound train of the day, x03 is the second northbound train of the day, etc. These numbers are placarded on the leading element of the train (either the control car, for northbound trains, or the locomotive, for southbound trains); the MP36-3C locomotives have electronic displays showing the train number (when travelling northbound, the locomotive number is displayed instead). The practice of placarding train numbers dates back to the Southern Pacific days.