The number 7 is often considered lucky in Western culture and was very prominent in ancient cultures. It is believed that hanging a horseshoe in a "U" shape above your door can bring good luck in and keep evil at bay. Traditionally they were held in place by 7 nails. considered to be the luckiest number.
777 is used on most slot machines to identify a jackpot. The number is considered so lucky that banknotes with a serial number containing 777 tend to be valued by collectors and numismatists. The US Mint even sells uncircled 777 $1 bills for this reason.
Bring yourself some extra fortune in this vintage style jackpot necklace.