It is not listed in
Brunk's 2003 book ─ the "bible" of modern countermarked coins. The list of countermarks is also available online; here are
letters P─Z. Note that unpublished countermarks are found all the time. I've just sent off to a journal a short note about a new countermark which I was able to trace back to the issuer.
There are 1000s of different countermarks and only a small percentage has been attributed to their issuer. Sometimes, even a full name
such as Thomas Peters is not easy to trace. It is obviously more difficult to identify the issuer when he used only initials. It is likely that issuers (bakers, blacksmiths, etc.) cared only for their countermarks to be recognized locally.
In your case, because the letters are well aligned, I think we have a single punch made locally of four letters instead of four separate letters punched individually onto the coin. Note also the depth of the letters increasing progressively to the right, hence the punch was held at an angle.
There could be two people:
T(---)
S(---) and
O(---)
B(---), or a single person:
Thoma
S O'
Brien comes to mind as a possibility. Because there are few first names starting with "O", I prefer the second possibility. Note that Thomas can be abbreviated T, Ts, Ths, or Thos. I don't think the
S here is a middle initial because we would then expect a dot between the
T and the
S, but these things are not always entirely logical, so that possibility should not be ruled out.
Because there is a dot in the middle, we know it's not
This
Son
Of a
B*tch.
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