This old white porcelain strain is marked P & S in that little white rectangle to the left above the groove. It has more lettering in the groove. According to Gerald Brown in his book: Collectible Porcelain Insulators Second Edition, Page 127, he acquired one 'and the patent date down in the wire groove. (Jan. 14, 1892)' While I cannot read my marking, it may say Pat Jun 1892??? A crude old-timer made by Pass & Seymour