there are a few old and new ones like that on the minster
i can think of a few sigs and "quirky" things from places i and colleagues have fixed up
my colour chart of 3 wks of mixing different shades of "pigeon" and trying them each day on the out facing corner of a rather nice building is signed and hidden behind a chimney
in a more normal way i have made my mark on half a dozen out of a few hundred if it seemed appropriate(appropriate is full control of means and intent)
only the ones with special quality would get a mark, a good job is just work
I am sure like us that the masons got bored with doing repeated designs, so perhaps they also put in little bits like that just to see if anyone noticed and for a bit of a change.