Deacon of Pndapetzim at English Wikipedia, Public domain, via Wikimedia Commons
No, it's not a particularly militant wing of "dog walker's poo bag" brigade. It is, in fact, a Clootie Well. This one is near Munlochy on The Black Isle.
"Clootie wells (also Cloutie or Cloughtie wells) are places of pilgrimage in Celtic areas. They are wells or springs, almost always with a tree growing beside them, where strips of cloth or rags have been left, usually tied to the branches of the tree as part of a healing ritual. In Scots nomenclature, a "clootie" or "cloot" is a strip of cloth or rag. As-in: “Ne'er cast a clout till May is out,” the old English meaning of the word clout, means cloth or clothing.
When used at the clootie wells in Scotland, Ireland, and the Isle of Man, the pieces of cloth are generally dipped in the water of the holy well and then tied to a branch while a prayer of supplication is said to the spirit of the well.
In Scotland, by the village of Munlochy on the A832, is a clootie well (called in Scottish Gaelic: Tobar Churadain) at an ancient spring dedicated to Saint Curetán, where rags are still hung on the surrounding bushes and trees. Here the well was once thought to have had the power to cure sick children who were left there overnight
The site sometimes needs to be cleared of non-biodegradable materials and rubbish such as electrical items and a venetian blind."