Not on is sapphire the September birthstone, it is also the stone traditionally associated with the 5th wedding anniversary (although more modern thinkers link it to the 23rd anniversary); and astrologers associate the sapphire with the zodiac signs Taurus and Libra, and with the planet Venus.  It's little wonder so many events, months, signs and what-have-you want in on the act when the sapphire is so pretty!