What is this man wearing?

[Mike Serpa]

A. B. Seavey - 15th N.H. Vols. Post-war photo? Secret society garb? Illuminati, Masonic, Skull and Bones, Druid, Rosicrucian, Knights Templar, DeMolay, Friends of Fluffernutter???

History of the Fifteenth Regiment, New Hampshire Volunteers : 1862-1863. Page 469.
by McGregor, Charles
Published 1900
https://archive.org/stream/historyoffifteen00mcgr#page/468/mode/2up

 

[chubachus]

Pretty certain that he is a Freemason. Here is the most similar type of masonic garb I can find in another 1800's photograph:

 

[GELongstreet]

Don´t know which regalia those are, as similar as those of the different organizations can be. But your source names several officers as masons and also has two instances of masonic meetings within the regiment and together with other units.

 

[Private Watkins]

He's an Odd Fellow.

Here's an image of another member of the Independent Order of Odd Fellows, or IOOF:

Beautifully hand-colored, half plate daguerreotype portrait of a bearded Odd Fellow wearing a long, gold-fringed apron decorated with embroidered flowers, leaves, crossed swords, and other symbols associated with the fraternal organization. Note the letters F L T within the three links that stretch across the gentleman's abdomen, which stand for the Independent Order of Odd Fellows' motto "Friendship Love Truth." Housed in half case, with inked identification under the plate Gilbert Schmitz.

And a couple of period Odd Fellow aprons:

 

[James B White]

The three chain links in the OP made me think of the Odd Fellows too.

 

[Dave Hull]

You all beat me to the punch. Our old Lodge building in Arlington sat on the south end of a block of businesses and the Odd Fellows Lodge sat on the north end of the block. According to the older members of our Lodge, the Odd Fellows used to get a better deal at the Little Tavern directly below their Lodge on the street level. I believe that particular Odd Fellows Lodge went dark in the 70's.

One of my old friends told me there was not much difference between the Odd Fellows and Masons (he was a member of both.)

 

[AndyHall]

Yes, Odd Fellows.

 

[Mike Serpa]

Thanks, y'all! Odd Fellows it is.

 

[MRB1863]

I find that answer NOT particularly odd...