From 1867 to 1904, the letter F was added to the usual sterling marks for foreign sterling silver imported into the UK. But from 1904, the F was dropped and was replaced by the decimal value of the standard mark and a special assay office mark had to be struck.
Such marks were different according to the particular assay office. In the case of London, it was a rayed sun with facial features. The leopard's head and the lion passant were also discontinued. I recently acquired a dish made in Hanau by Georg Roth & Co which is a good example of the above.

According to Dorothea Burstyn in her "The Antique Silver Industry of Hanau" article, Georg Roth & Co produced silver that leaned strongly on French styles - festoons and portraits in medallions are ever-recurring features.

My dish follows this admirably. It has typical Hanau fantasy marks stamped underneath, with the London hallmarks on top.
My interest in the dish was enhanced by the rarity value of the London import marks applicable from 1904 to May 1906 only. After this date, a different symbol was used for London imports from then on.

The sponsor's mark of GB is that of George Bedingham who first registered his mark in his own name in 1902. He is registered as a silver worker.
The date letter is "k" for 1905.

The dish is approximate 15cm in diameter and weighs 112g.