Maastricht, Holland is where Petrus Regout started his De Sphinx pottery in 1836. He started to sell pottery along with his crystal, and glass company that he formed in 1827. De Sphinx ran under the company name 'Petrus Regout & Co.until 1899. Petrus lived from 1801-1878. His sons inherited the company which merged in later years. You can read more about this online.
The image of the sphinx had been used since 1879. I do wonder about this date. Petrus, in 1836 'added an equally modernized earthenware factory" to his glass wares. It was known back in 1834 as The Royal Sphinx factory. Why use such a name if not using a sphinx image on the earthenware started in 1836? Just a thought as I try to date my shard.
The image of a complete trademark above is from 1883. If it is true that a sphinx was not used until 1879 as a pottery image, then my shard must not be older than 1879.