Unfortunately, those markings do not identify the type of gearbox on the motor. The color of the markings does indicate if the motor is a high-, medium-, or low-power motor, but the numbers and letters in the markings are not linked to the gear ratio. You might be able to differentiate between motors with different gearboxes by comparing their speeds. One way to do this is by powering each motor at a low voltage (2V would probably work) and counting the number of ticks the flat side of the output shaft makes against something like a table edge over a period of a minute. You could then multiply that number by 3 to get the RPM at 6V.