The Rolex Daytona, ref. 6265 in this post features a rare black Sigma dial with white subdials and a CRS marked caseback. A Sigma dial is a Rolex dial named for the letters printed at the bottom of the dial at 6 o’clock. Most Daytona dials are marked with “T Swiss T,” however a Sigma dial is marked “σ T SWISS T σ.” These Daytona’s get the name from the two O shaped symbols on each side of the “T SWISS T.” Dials marked with this lettering are fitted with solid gold markers, unlike other dials which may use steel or other materials. Sigma dials come in both yellow and white gold and are very rare. The watch is available here
It is common for many 6265’s to be fitted with a 6263 caseback at the Rolex factory. This caseback is also labeled with the initials “CRS,” which stands for Charles René Spielman, a case maker who supplied Rolex and Tudor for a period.