On the Mabuchi motors, the model is etched very faintly on the side of the can, but it's readable, usually. Johnson motors often (not always) have the model printed in blue ink, but can require a little detective work to narrow down the model.

Seeing how I've got time, a camera and a box of motors...

The first two pictures are Mabuchi 27 turn silver cans. the codes - TD048417 and TD049417 - are production batch numbers. They're not marked as a specific model otherwise.

The third picture is a Mabuchi 7520 (batch TD036Y21). It also has another number (contrast enhanced) that I'm fairly sure is a number for the end user. In this case, whoever made the vacuum I got this from.

The fourth picture is just for kicks. It's one of Doc Mertes' TCS legal Red Dots. Every one has a serial number engraved into it by the man himself! It's cool to have the artist's signature.