A very recent acquisition from a lineman's collection this small unmarked light grey porcelain signal has a dark spot on the crown. It appears to be a gob of dark brown glaze that has been fired with the insulator. Coincidentally, there is a small fracture of the porcelain underneath the dark brown gob. Click here for 2nd picture of bottom [id=309694135].

Ans: The porcelain insulators were fired on vertically stacked racks. Some leachates from the insulator(s) above probably dripped onto the crown of this porcelain signal.