Roman numeral
Omicron Ceti III listed on Anaanda Ziff's personnel file
The date of Starfleet Academy's incorporation into the Federation, 2161, is written out in Roman numerals on its official logo
Roman numerals were a system of numbers originating with the Romans.
As late as the 24th century, Roman numerals were sometimes used to classify planets' position from their primary star by Starfleet. (TNG: "Eye of the Beholder" et. al.)
The titles of Star Trek films 2-6 utilize Roman numerals to identify the film number.
While Memory Alpha always uses Roman numerals for consistency in naming pages (e.g. Denkir IV, they are only occasionally used in writing, and are more often spelled out. (i.e. four instead of IV)