The ring is said to have been given by Tsaritsa Alexandra Feodorovna (consort of Nicholas II) to an officer of the 5th Alexandrian Hussar Regiment of Her Majesty Empress Alexandra Feodorovna. Alexandra was an Honorary Colonel of The Regiment.
The skull measures 0.6 x 0.6'' (1.6 x 1.6 cm), and is made of silver over gold and set with 59 old mine and rose-cut diamonds. The gold ring is a US size 7 and measures 0.7'' (1.8 cm) in diameter. The prize for it is 12,500 USD, and you find it at Romanov Russia.
And this is what the badge and the uniform of the Alexandrian hussars looked like.