Just had a "Duh" moment.

[DOOM!]

I just realized that Lego uses the set number for the licence plates on thier vehicles. It is probably common knowledge for a lot of collectors but I had never made the connection until today. Kinda cool. :)

Edited November 29, 2019 by DOOM!
Typo

[Rudivdk]

Yup, and sometimes they also use letters instead of numbers (S for 5 for example).

For some time they even made a logo for certain vehicles in the Technic theme, consisting of a stylized L and T (Lego Technic). Took me some time back then to realize that as well.

Also often seen in Technic is the initials of the (main) designer +setnumber as license plate. There are lot of references to be found in sets when looking for it.

[icm]

Not just license plates, but also registration numbers and hull numbers on ships and aircraft.  This goes all the way back to Classic Space in 1979, where the spaceships in kits 918, 924, 928 had bricks printed with "LL ###".

[The Reader]

Concerning this film

(from 35:20 min on) set 60110 was designed by Lego designer Henrik Andersen. That's why his initials "HA" together with the set number are on the number plate of the fire truck.

[Axelford]

Also about the spaceships with LL... with their set number. LL stands for LEGO land and is also used in airport sets as a registration.