PS - Professional Surveyor. Those markers are part of the BLLM (Bureau of Lands Location Monument) so definitely they are not treasure markers. They were being placed there in lieu of the cylindrical cement due to the topographical erosion which could alter the the exact location. The stones are seen as permanent so it was chosen rather than the use of the cylindrical cement. That method is still adopted until 1976 or 1977.
In the book of Engr Venancio Besavilla, (Reviewer on Math and Surveying- 1976), it used the words Philippine Survey but some old professional surveyors still prefer Professional Surveyor.
Whew, this topic made me run and look for my old books!!!