From the Josh Greenwood Collection.
The S anvils have several distinct features.
The rectangular handling hole (all others are square or nearly square), the sloped face and the shape of the fifth foot.
A study of other collections indicate that the French use rectangular handling holes and this may indicate a French influence or background to the "S" anvil maker.
The sloping face is curious as it is severe enough to have been obviously made that way on purpose.
But for what purpose?
We can only speculate.
While these fifth feet are not exactly alike they are more alike each other than to other brands.
Since anvil making at the time was largely all hand work by teams of anvil smiths the character of each piece of their work would be similar.
The differences in the two pieces above could also be attributed the passage of time.
Skills develop and change, members of the team come and go.
See The Mystery of the 5th Foot
Conical Horn Colonial "S" Brand Anvil
Hornless Colonial "S" Brand Anvil
Old English S Anvil
From the Andy Mason Collection, UK.