Hi,
Peter is right about the maker:
Gebruder Dingeldein (Dingeldein Brothers), Hanau firm was founded in 1868 by brothers Friedrich Otto (ca. 1838-1901) and Freidrich Wilhelm (ca. 1838-1910) Dingeldein. Friedrich Otto's son August Ernst Dingeldein (1874-1962) was their successor, and married Margarethe Kurz (1876-1947), the daughter of Karl Kurz (1851-1936), which is how the Dingeldein and Kurz companies came to be merged in 1911. He did open a New York showroom assisted by his sons Karl August (1901-1965) and Otto Friedrich (1906-1991) Dingeldein, both of whom moved to America permanently in 1927, where they became prominent silversmiths in New Orleans, Louisiana and Cape Girardeau, Missouri, respectively.
I suppose your cup is made between 1901 - 1921 because the same set of pseudo British marks is often seen with Austria - Hungary import mark (far left), which was used 1901 - 1921. Also meaning, your cup was made in Germany (Hanau) i.e. before they moved to America. Otherwise, Austria - Hungary import mark would be illogical.
Regards