Great Seal of the Commonwealth of Massachusetts

The Great Seal of the Commonwealth of Massachusetts is not the most elegant of state seals. Most state seals are cluttered and Massachusetts' is cleaner than some (I'm looking at you, Wisconsin, Oregon, and Hawaii), but it still has a lot going on. There's no harmony between the elements: a random star, an out-of-proportion arm floating vaguely above the shield, and a wordy, counterclockwise banner surrounded by clockwise Latin outer ring.* At least Massachusetts' seal only uses four colors — Montanans and Californians need the big box of Crayolas.**

Massachusetts' seal features several elements:

a shield having a blue field or surface with an Indian thereon, dressed in a shirt and moccasins, holding in his right hand a bow, and in his left hand an arrow, point downward, all of gold; and, in the upper corner of the field, above his right arm, a silver star with five points. The crest is a wreath of blue and gold, on which in gold is a right arm, bent at the elbow, clothed and ruffled, with the hand grasping a broadsword.

The motto, "Ense petit placidam sub libertate quietem" ("By the sword we seek peace, but peace only under liberty") was written by Algernon Sidney, presumably sometime before he was executed for treason.

My favorite part of the seal has always been the disembodied arm swinging the sword. There's a Massachusetts monument at Gettysburg that has an arm rising out of the top — when I was a child, it always made me think of zombies.

According to the Secretary of the Commonwealth, the sword was first added to the seal in 1775, but it doesn't seem to have become disembodied until at least 1780. Yet, we find it on the Benjamin Chamberlin gravestone in Pepperell, MA (dated 1778):

There are a few possibilities here:

• the arm and sword motif may have been circulating in Massachusetts before Nathan Cushing designed the seal in 1780
• the Benjamin Chamberlin stone may have been carved after 1780

Has anyone seen the arm and sword on an object that can be positively dated pre-1780? If not, the second possibility seems more likely. It might help me determine how long it took for communities to erect gravestones for men who died far from home during the Revolution.

THIS MONUMENT

Is Erected in Memory of

Mr. Benjamin Chamberlin

who departed this Life

in the Continental Army

at Valleyforge in the

year 1778; In ye 17th

year of his Age.

He was ye Son of Mr. Phineas Chamberlin

and Mrs. Lydia his wife.

*I say this, of course, with the caveat that I know nothing about heraldry. It may fit the conventions very nicely, but I still think it's ugly.
**The best state seals (in no particular order): Rhode Island, Texas, Louisiana. Mississippi would be a contender if they hadn't just lifted their design from the US seal.