Randomly poking at TESS (USPTO database) found these live trademarks (ignoring the dead): NGC PCGS (Collectors Universe, Inc):
Name of the other bison that could have been the model for the Buffalo nickel. Though it's frequently said that the model was Black Diamond the horns on the Nickel point the wrong way.
So PCGS trademarked Black Diamond first and NGC went for Tatanka just in case? And thanks for the answer @Jaelus and Burton!