Some like to number their documents to match SQF's scheme. I personally don't like it because when a new standard gets published (like edition 10 later this year), you have to redo your entire program. However, I've always liked the 4 digit identifier system, just written to my own book and not specific to their requirements.
Take 19.0.0.0 as an example. First number is a "chapter" in my FSQMS, 19.0.0.0 would be the Program document broadly describing my maintenance program's requirements. Second number represents the SOP's, so 19.1.0.0 might describe the SOP for equipment PM's, 19.2.0.0 might prescribe frequency for all listed equipment in my facility, etc. Third and fourth digits get into more specific SOP's, so 19.1.1.0 might start the SOP's for specific pieces of equipment, and I can always add a document in between 19.1.1.0 and 19.1.2.0 by labeling it 19.1.1.1 (say an extra piece of info is needed for that first piece of equipment).