I was given a link to the 1944 edition of TM-E 30-480, Handbook Japanese Military Forces and Chapter XII, §1(2)(b-d)http://www.ibiblio.org/hyperwar/Japan/I ... 12.html#II which kind of answer that question, but at the same time implies a Japanese officer would have to mix between Kanji, Arabic, and Roman numerals in addition to using the English alphabet for abbreviations, and that just doesn't seem correct given the pervasive xenophobia.
b. Military abbreviations. (1) English letters,both capital and small, normally are used in military abbreviations.
(2) The basic army abbreviations appear in most cases to be derived from German words and, in the case of most recent additions, romanized forms of Japanese words. For example: BA (Bergartillerie), mountain artillery; SeE (Sempaku eiseitai hombu), shipping medical unit headquarters. (3) Naval abbreviations are derived largely from English words and less frequently from romanized forms of Japanese words. For example: BC, battle-cruiser; cdg, combined destroyer group; AtB (Attached "butai"), attached force.
c. Numbers. The numbers of units and weapons are shown by placing the appropriate figure, either Arabic or Japanese, with necessary additions, in parentheses after the particular sign or abbreviation. For example (2), two airplanes; A () three battalions of field artillery (the two characters in the parentheses are, respectively, "three" and the first character of the Japanese word for "battalion").
d. Identification. (1) When it is necessary to distinguish between enemy and friendly forces, the Japanese show signs for the former in red, for the latter in blue.
(2) In indicating the organizational numbers of units, Arabic numerals usually are used for all units except battalions, for which Roman numerals are used. The number of the lower unit precedes that of the higher organization of which it isi a part, the two being separated by a slanting line. For example: 18 P, the 18th Engineers; III/2i, 3d Battalion of the 2d Infantry Regiment. II St/1A, 2d Battalion Ammunition Train of the 1st Field Artillery Regiment.
(3) Platoons and sections usually are shown as fractions of a company. For example: 1/42/1P, 1 platoon of the 2d Company of the 1st Engineer Regiment; 1/162/5i, 1 section of the 2d Company of the 5th Infantry Regiment.
(4) Missing units of an organization are indicated by numerals, preceded by a minus sign, in parentheses. Units attached to an organization are shown similarly with a plus instead of a minus sign. For example: 2ii(-7.8), 2d Infantry Regiment less the 7th and 8th Companies; 1(+iP)/2i, 1st Company, plus a labor unit, of the 2d Infantry Regiment.