My 624LH has a serial number thus: ALWXXXX.
The former owner must have sent it in (I've had it for a long time) because it has the Circle C on the box.
The circled "C" on the grip frame is on a number of S&W revolvers I have seen. It would seem not to be a record of the recall.
Mine also has the "F" stamped on the rear face of the cylinder. I have no idea what it might signify.
S&W 624 Lew Horton Special Right.jpg