OK, I wrote to the lady who wrote the article about Adam Henderson and got a very nice reply back from her... The spoon evidently was NOT made by A Henderson. The reason I inquired her was because of no name on the spoon where the example in her article had A Henderson on it. So I thought perhaps it was the mark of his former employer, or that at least that was an indication it was an older spoon due to no name, but evidently not the case. Here is her reply: Thank you for your email inquiry as a result of reading my article about Adam Henderson.Did you read article online at Silver Society of Canada website?
A fun coincidence that your friends found 2 similarly marked spoons varied places such as NY State and on Cape Cod!
Those two spoons have 3 pseudo-hallmarks (eagle-arm & hammer- bust) which probably were used by some coin silver maker in Orange County, NY (Newburgh or Middletown), on the opposite side (SW) of the Hudson River from Poughkeepsie.
That unidentified maker is said to be after 1830 in John R. McGrew's book, Manufacturing Marks on American Coin Silver.
This is the considered thinking of other silver historians as well.
Why no one knows for sure - Orange County 19th C. manufacturing census records lost in fire. Thus, only conjecture as to maker who used those marks.
The 3 pseudos were probably not the mark of Adam Henderson.
Certainly, they are not the mark of George Halliwell.
Since your 2 pseudo marks are on spoons that date from Adam Henderson's 1840's - 1850's period; we can date your spoons to mid-19th C.
They are not of a very early date.
In the top spoon photo you sent me - I cannot tell if it is dirt or a name on the stem along with the 3 pseudos. Name?
In my article, I was concentrating solely on marks used by Adam Henderson - not the specialized study of pseudo-hallmarks.
That is a whole other discussion.
I enjoyed hearing from you, Kay Olson Freeman