Hi Dave,
I'm in Medfield and so is the house/barn. A bit if trivia...way back when, Medfield got "crowded" so the town fathers sent forth settlers to find a new Medfield and some of them settled in Sturbridge, which was for years called New Medfiled. We have ties to Deerfiled as well. You can Google the Dwight-Derby house if you're interested. Its one of the oldest homes in the country, built in 1651. Original owner was shot by an arrow from King Phillip's native Americans when they attacked the town and burnt most of it down in 1676.
We think the barn was built around 1800, but we're not sure. We had a stack of old boards in the second floor of the barn that are pit-sawn, gang sawn, band sawn and circular sawn. Many of the posts and beams seem to have been re-used here as they have lots of now-unused mortises, etc. and Roman numerals on floor joists with none on the beams into which they tie.
Interestingly enough, the post with the unique mark is on the east corner, but its probably 4' from the top, so its not a 2 foot mark. We didn't see any double line marks on the west corner post. I'll take a closer look. We are only going to re-shingle the front and right sides of the barn so we're not tearing off other shingles and sheathing just to see if they have marks as well.
I found this site: http://www.dbrg.org.uk/Marks/Cmarks.pdf which shows this mark, but not as a standalone mark. This site is in England and Medfield is thought to have been named after Metfield England. Looks like builders didn't want to have Roman numerals reaching into the hundreds, so they sometimes added a mark like mine to one of the numerals to the I after a V to differentiate it from a plain old VI (6), thereby reducing the number of numerals. Makes sense, otherwise a barn frame would look like the credits on a movie where the date is MCMXXXVI!
Thanks for your reply.
Harry