2006-S NGC PF70 Clad Proof State Quarters 5 Coin Set All five 2006-S Proof State Quarters, a complete year set, NGC certified PF 70 Ultra Cameo. 70 is the highest grade awarded by NGC. State Quarters issued in 2006: Nevada, Nebraska, Colorado, North Dakota and South Dakota. NGC is Numismatic Guaranty Corporation. "S" mint mark coins are from the San Francisco Mint. Quantities are limited, so order now! Add this investment quality set to your collection! Click on picture to see larger view in pop-up window.