The para­graph mark (¶) is used when cit­ing doc­u­ments with se­quen­tially num­bered para­graphs. The sec­tion mark (§) is used when cit­ing doc­u­ments with num­bered or let­tered sec­tions.

A para­graph mark or sec­tion mark should al­ways be fol­lowed by a non­break­ing space. The non­break­ing space acts like glue that keeps the mark joined with the nu­meric ref­er­ence that follows.

With­out the non­break­ing space, the mark and the ref­er­ence can end up on sep­a­rate lines or pages. This can con­fuse readers.

If the para­graph or sec­tion ref­er­ence comes at the start of a sen­tence, don’t use the mark—spell out the whole word (Sec­tion 17200 ap­plied to the trans­ac­tion, but § 17500 did not). In a ref­er­ence to mul­ti­ple para­graphs or sec­tions, dou­ble the mark (¶¶ or §§).

Though these marks are used most fre­quently by le­gal and aca­d­e­mic writ­ers, there’s no rea­son oth­ers shouldn’t use them (See § 31.4.2 of the man­ual). Why not? They look cool.