In my schematics, I like to add components that are not necessarily mounted on the PCB to ensure that they are captured in the Bill of Materials (BOM) output by my CAD tool.
These might include the PCB itself, an enclosure, screws, standoffs, light pipes, cables, etc.
It’s useful to capture all these in a BOM that is well controlled so that kits are built up correctly and nothing is overlooked.
I am wondering if there are standard Reference Designators that people use for these items.
Right now, I use:
PCB for a PCB 
ENC for an Enclosure
MP for a Mechanical Part, e.g. a screw or standoff
Are there any standard alternatives that people use for these?
Any suggestions on a Reference Designator for a Light Pipe. MP doesn’t seem quite right but it does do the trick.
Also, any suggestions on a Reference Designator for a cable, e.g. USB cable.
Happy to hear any suggestions that people might have.
Thanks