SH capital letters stamped with a bird is the mark of Sheryl Holstein of Mountain Oak Pottery.You will see what is likely a progression with this mark.
1) If you look at the one on The Marks Project, the letters are very fancy and the bird is very detailed. This seems likely to be a late mark. https://www.themarksproject.org/marks/holstein
2) If you look at this one from seller reduxion55 on ebay the letters are the same as above and the bird is still an outline, but a better one than the one below. This one is likely earlier than (1) above.
3) If you look at this mark to the bottom right, the bird is definitely incised by hand, it's just an outline (an incomplete, and the letters are basic block capitals. This is probably the earliest of the three marks, and the piece it was found on is very simple.
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