Now available as a 79 page PDF file at the following link.
The Briere Survey, 2011 edition
These markers were erected in 1930, as documented by a Commonwealth publication titled Historical markers erected by Massachusetts Bay Colony (1930) (http://www.archive.org/details/historicalmarker00mass).
Also available here is a short 2011 slide presentation entitled Roadside Marker Inventory Presentation November 2011