46 CFR §50.10-25

1. (a)The term Coast Guard Symbol means that impression stamped on the nameplates of boilers, pressure vessels, and safety valves by a marine inspector upon the satisfactory completion of the tests and inspection of the product. It may also be used by a marine inspector to identify workmanship test plates and welding samples.
2. (b)The impression of the Coast Guard Symbol for stamping nameplates and specimens is shown in figure 1 to § 50.10-25(b).