It was the tribe of Dan, also known as tuatha de danann that founded Denmark, thus the name Dn Mark. The tribe of Dan traveled by ships all over the place and marked their tribe name in many places they established. http://www.british-israel.ca/Dan.htm

It is interesting that when translated, Dan = judge, but Daniel = God is Judge. Also, that the standard, also known as flag, of the tribe of Daniel is an eagle with a serpent in their claws. Numbers 2:2 KJV

"Unquestionably the Danites can be traced more easily than any other Israelitish tribe because of their custom of attaching the name "Dan" to places and rivers along their line of march. Doubtless it was this family characteristic to which their great ancestor Jacob referred in Genesis 49:17 - "Dan shall be a serpent by the way." In other words, Dan in his wanderings shall leave a trail like a serpent. In fact, one translator renders it, "Dan shall be a serpent's trail." Judges 18 supplies two examples. Danites went and took Kirjath-jearim: "wherefore they called that place Mahaneh-dan." They passed on and captured the city of Laish, "and they called the name of the city Dan, after the name of Dan their father." Ptolemy's map of Ireland shows the names Dan-Sowar and Dan-Sobairse on the northeast coast where colonies of Danaan settled after departing from Greece in ships. Trace their land route northward out of Greece and the first thing one finds on the map is the river Danube. Follow the river on to the north, and a country called Denmark in English; Danmark in Danish, Swedish and Norwegian; Danemark in German and French; and Danio in Esperanto. According to the historian Keating, "The Danaans were a people of great learning and when they left Greece... and went to Ireland, and also to Denmark and called it Danmark, Dan's country." 'One Man's Destiny' by CR Dickey page 214.

"There is no grander theme upon the scrolls of history than the story of this struggle of the Anglo-Saxons westward. The very streams of Europe mark their resting places, and in the root of nearly all their ancient names (Dan, or Don) recall the sacred stream Jordan river of rest-- from whose whose hands, so far away, as exiles, they set out. It was either the little colony of Dan, obeying its tribal proclivity for naming everything it captured (Jud.18:1-29) after their father, or else the mere survival of a word and custom; but, none the less, it serves to TRACE these wanderers LIKE A TRAIL. Hence the Dan-ube, the Dan-ieper, the Dan-iester, the Dan-au, the Daci and Davi, the Dan, the Don, the U-Don, the Eri-don, and the THOUSAND OTHER Dans and Dons of ancient and early geography, down to the Danes in Dan-emerke, or 'Dan's last resting place'" (quoted in Allen, Judah's Sceptre and Joseph's Birthright, p.263-64).

Denmark, the name of the modern country in Europe north of Germany, means, literally, "Dan's mark." It's people are called "Danes." In fact, because at one time Denmark ruled all the surrounding region, the whole region took its name from them the ScanDINavian peninsula! Clearly, here are remnants of the people of DAN, who migrated westward overland from the Caucasus to their present location in northern Europe! “According to late Danish tradition... Jutland [the mainland of Denmark] was acquired by DAN, the... ancestor of the DANES” from whom their name derives (“Denmark,” Encyclopaedia Britannica, 11th ed., vol.8). The Danes claim the descend from "Dan the Great" meaning Dan of Israel (Saxo Grammaticus; "The First Nine Books of Saxo Grammaticus of the Danish History).

The third batch of Danites left a trail to their final homeland Denmark. As you can see the Serpent's head (Denmark) is the final destination of this tribe.