CHRONOGRAM
Etymology
Noun
chronogram (plural chronograms)
A sentence or inscription in which the capital letters, interpreted in Roman numerals, stand for a particular date if rearranged.
Source: Wiktionary
Chron"o*gram, n. Etym: [Gr. chronogramme.]
1. An inscription in which certain numeral letters, made to appear
specially conspicuous, on being added together, express a particular
date or epoch, as in the motto of a medal struck by Gustavus Adolphus
in 1632: ChrIstVs DVX; ergo trIVMphVs. - the capitals of which give,
when added as numerals, the sum 1632.
2. The record or inscription made by a chronograph.
Source: Webster’s Unabridged Dictionary 1913 Edition