[sandworm101]

A bike without an odometer is "true mileage unknown" (TMU) which makes selling/insuring/valuing it somewhat difficult. On a custom chopper that is normal. Many choppers don't even have speedometers. But on a normal bike missing such instruments is seen as a red flag that the bike is stolen and/or made from stolen parts.

[latchkey]

odometer value is easily modified, even with digital ones. Even then, it is often not accurate at all, especially on motorcycles, due to the fact that it is usually driven by a cable attached to the front wheel (just disconnect the cable and number never goes up).

[sandworm101]

Maybe in the 1980s. On a modern bike it is integrated into the transmission, usually on the drive sprocket. And then the signal is used in slightly different ways, with the odometer being accurate and the speedometer generally reading a few % higher than the actual speed. Some bikes may also use it for electronic engine/emission controls too.

[latchkey]

Not all bikes. 2023 DRZ 400sm still has a cable (they haven't modified the design in years). Most scooters/motorbikes are cables too.

Even still, it is easily hacked on almost any vehicle (Tesla is a great example of a connected car making it much harder) and there is plenty of YT all about it...

https://www.youtube.com/watch?v=hfPm-9p0YUI

https://www.youtube.com/watch?v=1MFd7Ufe7v4

https://www.youtube.com/watch?v=8wygJwWnFm4

https://www.youtube.com/watch?v=7Q_AMBBNk2A

When I was living in Vietnam, I could pay someone about $5 to do it for me.

What I learned pretty quickly was that the ODO is the last thing I'd rely on for price.