This article studies the duplication diacritic of Epigraphic Mayan (ISO 639-3 emy) during the Classic period (a.d. 200–900). Cataloged as grapheme 22A, it consists of two dots optionally and rarely affixed to another grapheme to command the reader, in the majority of cases, to read a syllabogram twice in sequence. This article reviews prior literature on the diacritic, elaborates a typology of four distinct but ultimately related functions, and employs a data set compiled by means of the Maya Hieroglyphic Database to determine via statistical tests whether scriptal, linguistic, media, geographic, and temporal factors were influential in its distribution, and more narrowly, its various functions. The results indicate that two lexemes, käkäw ‘cacao’ and k'ahk’ ‘fire,’ account for several of the scriptal and linguistic traits that show significant relationships with 22A, with the former, käkäw, likely serving as a major prototype in the evolution of 22A. It is also pointed out that 22A is absent from the Postclassic (a.d. 900–1521) codices, suggesting that one of the Classic regional subtraditions with lowest frequency of use of 22A may have been a direct ancestor of the subtraditions responsible for the codices.