That gun falls into the category known to collectors as the pre-war commercial, a common gun.* The serial number is 130904 and is in the normal places. The "96" over the "U" is not "96", it is a crown. The "C9C4" is actually "0904", the last four digits of the serial number. The "904" is the last three digits of the serial number. (Only the last digits of the serial number were used when the part was not large enough for the full serial number.)
The "NS" stands for "Neue Sicherung" or "new safety."
The markings on the bottom of the barrel are factory inspector's marks; they had no meaning outside the factory.
The S. F. L. 76 would appear to be a unit marking, but it is not shown in my records of German markings. Since the C96 was used all over the world (but used by Germany only in the 9x19 ("Red Nine") version) the marking could mean almost anything. Maybe someone else can help.
*The serial number is also in the "Red Nine" range, since those pistols were numbered in their own series, but the grips are obviously not "Red Nine". However, check the rear sight leaf; it should go to 1000, not to the 500 of the "Red Nine."
Jim
