Officina

Officina (Latin, plural officinae) were workshops within Roman mints.  During the early 3rd century Roman numerals I - IV were placed in the reverse fields of coins struck at the Rome mint to indicate the the officina within the mint that produced the coin. Most Roman coins struck after 274 carry officina marks, sometimes in the reverse field, but most often combined with the mintmark. At western mints the marks P, S, T, and Q indicated the prima (1st), secunda (2nd), tertia (3rd), and quarta (4th) officina. At eastern mints Greek numerals were used to indicate the officina from A (1st) to IE (15th). 


Chart of Officina Numbers

1st

I, P (for prima), PRIMA, A (alpha), OFF P (officina prima)

2nd

II, S (for secunda), SECVNDA, B (beta), OFF S (officina secunda)

3rd

III, T (for tertia), TERTIA, C, G (gamma)

4th

IIII, Q (for quarta), QVARTA, D, D (delta)

5th

V, E (epsilon)

6th

VI, V (stigma - archaic Greek letter resembling S)

7th

VII, Z (zeta)

8th

H (eta)

9th

N, Q (theta), DE (delta epsilon)

10th

X, I (iota)

11th

XI, IA (iota alpha), AI (alpha iota)

12th

XII, IB (iota beta), BI (beta iota)

13th

IG (iota gamma), GI (gamma iota)

14th

ID (iota delta), DI (delta iota)

15th

IE (iota epsilon), EI (epsilon iota)


Also see:
Officinae (by Doug Smith)
Antioch officinae (by 

Gert Boersema)

Officina Monetae (Dictionary or Roman Coins)
Mint marks

Sources:
Harl, Kenneth W. Guide for Coins Commonly Found at Anatolian Excavations, Roman (A.D. 238 - 498). (Istanbul, 2001).