Gujarat High Court Civil Manual (subordinate court practice), 1960
Correspondence shall be classified under four major heads, namely, (A) Judicial; (B) Administrative; (C) Finance and (D) Works. Each major head shall be sub-divided according to the list appended hereto. Every letter, memorandum, etc., shall bear the mark, A, B, etc., and the serial number of the minor head of the subject; e.g.; correspondence pertaining to contingencies shall be shown 'C3' and when any communication relating thereto is issued, it shall bear the mark 'C3' followed by the outward number and year, and the date, e.g., C3-50/1960, dated the 1st February 1960.