Carvings on stones and placing them in open is Buddhist belief of prayers and wishes to go heaven.  Almost every monastery has these stone which are standalone example of highest degree of art embedded into religion.
Mostly Om-Mani-Padme-Hum but other prayers and wishes are also part of Buddhist practice of faith.
We found such stones , some of them seems to be decades old, almost everywhere in Thangi. Near temple, on way to temple and even inside village, alongside roads.