Brother accused of locking down third-party printer ink cartridges via forced firmware updates, removing older firmware versions from support portals [see comments]
It's a feature that can be turned on the confidential documents but I don't think it's actually on by default.
You can check for it anyway, just print a document then attempt to scan it, if it's got the track marks it will refuse to scan because one of the things the track marks do is block scanning, although you can still take a photo of it because the camera probably won't be able to see the track marks so it's not 100% secure. In fact it's largely considered an obsolete security method these days, along with pink flimsies.
I know about the yellow dot thingy. Literally metadata on paper for no reason imo. I highly doubt a person could make a realistic fake through the use of a conventional printer.
In the UK, we don't even have paper money anymore, it's plastic... Maybe it's more of a USA skill issue, too?