Introduction

Regular symbols numbering looks something like this: R1, R2, R3, R4

🔋 TP4056 Li-Ion USB Type-C charger
Simple 555 LED Blinking (Pulse generator circuit with simulation and PCB)

But for bigger electrical and other circuits, that consist many separate hierarchical sheets, it is more reasonable to do the numbering in the form, that contains sheet number, like this: R1201, R1202, R1203, R1204

Examples

You could see this enumeration type in electrical schematic diagrams of consumer electronics (complex devices with big schematic sheets quantity):

Apple iPhone XS
Apple iPad Air
Xiaomi Mi Notebook 15.6 Pro

KiCad

I recently change current projects to this type of numbering because many CAD systems support it, including KiCad.

It works very simple, just change default Numbering in Annotate Schematic window to First free after sheet number X 100

All done, previously it has regular designators:

Now schematic symbols references updated to the new numbering style, that includes sheet number (in this case schematic sheet number is 2):

Conclusions

• This allows you to make symbols of the schematic (sheets) more modular, because when it  integrated into other projects, only the first two digits (page number) could be changed

• Much more easier to navigate if you only have a just schematic and silkscreen designators on board or assembly drawing

• The main disadvantage is extend Ref takes more space on silkscreen layer of the board