The name Jamar ranked 626th in popularity for males of all ages in a sample of 2000-2003 Social Security Administration statistics and 859th in popularity for males of all ages in a sample of the 1990 US Census.
Though this name appears on the 1990 U.S. Census lists, it is used by only a small percentage of the general population.
Mars was the Roman war god, equivalent to the Greek god Ares.
Though Marcus (derived from Mars) was certainly a source for this name, a Mark from the Netherlands drew our attention to an Ancient Germanic influence as well.
Terms for boundaries in various Germanic languages, such as the Old English mearcs, gave rise to the French surname (and title) Marquis, and the surnames Marks, Marx and March among the English, German and Dutch. Those surnames and their sources undoubtedly contributed to the emergence of Mark as a personal name.
Borders being traditional points of conflict, it is fitting that words with such a meaning should converge with the name of the Roman god of war to give us the modern name Mark.