Sarreguemines is an incredibly famous french pottery factory in a town of the same name which changed nationalities several times; in German the town is known as Saargemünd but whilst you can find pottery stamped Sarreguemines, you'll never find a piece of pottery stamped Saargemünd.
During the time Sarreguemines (the place) was a German territory, Sarreguemines (the factory) was run by its director a man named Paul Utzschneider.
If the backstamp on ceramics therefore is "Sarreguemines" that means it was produced either before the territory became German, or after it reverted back to France in 1918... but, if it is marked Utzschneider & Cie it was produced in the 50 year period 1870-1918.
Same factory, utterly different names and naming convention. Yes, porcelain mysteries are like women... enigmatic.
More Reading:
From their webpage Steinmarks
Porzellanfabrik Utzschneider & Cie - Sarreguemines
Sarreguemines, Lorraine, France. Became Saargemünd, Elsaß-Lothringen, Germany in 1871. Reverted back to France in 1918.
Steingut- und Porzellanfabriken / Manufacture of earthenware & porcelain
The pottery was founded by Nicolas-Henri Jacobi in 1790, but Paul Utzschneider took possession of the factory in 1800. The business is still operational.Paul Utzschneider b.1771 - d.1844