God Himself told Ephraim to mark their way so that they could return one day to the Promised Land: "Set up signposts, make landmarks; set your heart toward the highway, the way in which you went. Turn back, O virgin of Israel, turn back to these your cities" (Jeremiah 31:21). How were they to do this?
One of the main ways involves the prophecy of Jacob about the tribe of Dan. "Dan shall be a serpent by the way, a viper by the path" (Genesis 49:17). A serpent or snake leaves a mark behind it as it moves over the earth; some snakes, like rattlesnakes, leave very distinctive trails. So does the tribe of Dan.
Though Joshua had allotted land to Dan in Canaan, the Danites found it to be difficult to hold and settle because of its proximity to the Philistines. They began to look elsewhere for living space.
And six hundred men of the family of the Danites went from there, from Zorah and Eshtaol, armed with weapons of war. Then they went up and encamped in Kirjath Jearim in Judah. (Therefore they call that place Mahaneh Dan [Camp of Dan] to this day. There it is, west of Kirjath Jearim.) (Judges 18:11-12)
Finally, they came to the city of Laish, in the far northern reaches of Israel, and they took it. "And they called the name of the city Dan, after the name of Dan their father, who was born to Israel. However the name of the city was formerly Laish" (verse 29).
And thus they have been naming places after their ancestor ever since! A good map of Europe will show dozens of place names carrying the name of Dan within them. The Don, Dnieper, Dniester and Danube rivers all flow into the Black Sea. The Romans knew the Rhine and Rhone rivers as the Eridanus and the Rhodanus. Denmark (literally, "Dan's Land") and Sweden are both northwestern European countries. The English escaped from Dunkirk (literally, "Dan's Church") during WWII. One can find similar place names sprinkled heavily throughout England, Scotland, and especially Ireland, where dun means "judge," just as dan does in Hebrew!