What does Boxing Day have to do with boxing?
Old English mearcere "writer, notary" (glossing Latin notarius "clerk"), literally "one who marks," agent noun from mark (v). Not found again until late 15c., hence modern use is perhaps a separate formation. Meaning "monument stone" is from 1888. Meaning "felt-tipped marker pen" is from 1951, so called because their purpose was to "highlight" text.
marker mark·er (mär'kər)
One that marks or serves as a mark.
A physiological substance, such as human chorionic gonadotropin or alpha-fetoprotein, that may indicate disease when present in abnormal amounts in the serum, as that caused by a malignancy. Also called biomarker.
A genetic marker.