Older 35mm eastman MP film sometimes had an inked footage number every 18 inches, the first letter of that number indicated the film type. 12 frames may not show the number. Later film has it as a latent image, also every 18 inches (1 Second for a movie) The latest film has a bar code with a string of digits, the first two letters indicated the type (for Kodak it would be Kx or Ex) but those don't have the strip numbers ie (Eastman 27 S'afety Film)