Stampings like these on Gold are in reference to the alloy mixture of the piece of jewelry or "Karat" of the Gold.  In everyday terms we are used to refering to gold as 14 karat or 10 karat and so on.  The number 417 gives a more accurate indication of what the alloy consist of. 

Gold will range from 1 karat to 24 karat with 24 karat being 99.99% pure gold.  Therefore you can determine the amount of pure Gold in a piece by dividing the karat by 24.  For example if we have a 10 karat gold chain, 10/24 = .41666 or simply put for stamping purposes 417. Or the opposite if we have a piece stamped 584, then .584*24 = 14.016 or 14 karat.

It is a common practice to round these numbers for the purpose of making it easier to stamp them on smaller pieces or as to not take away from the glamor of the piece.