[Jim McDougall]

I found an entry on in "History of Manufacture of British Swords" by Harvey Withers, where he states that the Shotley Bridge makers '..impressed a running horse mark" in imitation of the running wolf.
The attached image is from a Revolutionary war period infantry sword found online, which is contemporary for the 'bushy tail fox' swords by Samuel Harvey.

It is interesting to see that the horse mark is really not the same, and suggests that at some point Shotley may well have been making cutlery in the 18th c.
At the same time, this marking, which seems similar even if not the same, and may be misinterpreted as a horse rather than BTF.

It does appear that Shotley, actually Oley, was providing blades to Birmingham in the 18th c. about the time of Harvey, but Harvey was known for the BTF (= bushy tail fox) with his initials SH on the body (though some are blank, some have only H).
While makers in Birmingham were producing munitions grade blades, it would seem that Shotley had become more diversified by then, and perhaps these serving knives were among their products.