There's a tale...
After Elen had accomplished her wandering through the word, she placed a Cairn at the end of the Sarn Elen. Her path then led her back to the land between evening and morning. From this Cairn originated all stones that direct the way at crossroads up until today.
( From a Celtic Myth)
Celtic "Cairn" = "Stone"
"Sarn" =" Path"
"Elen, Helen" = "Goddess of the Roads"
There is more to this tale.............