Where does “mærki” come from?

mærki (Old Swedish) comes from Old Norse merki, from Proto-Germanic markō, from Proto-Indo-European morǵ- — edge, boundary, border; frontier, border.

Ancestry of “mærki”, step by step

Step	Language	Word	Meaning
1	Old Norse	merki	boundary
2	Proto-Germanic	markō	border, boundary; region, area
3	Proto-Indo-European	morǵ-	edge, boundary, border; frontier, border

mærki — Etymology, Origin & Word History | Etymology Explorer