The following explanation is for non-English speaking readers.
The English term “sound” means an audible “sound,” and it can also mean “solid.” Therefore, the brand claim “make money sound again” can be translated in two ways:
“Make money sound again” or
“Make money solid again”
For flexgold, this ambiguity focuses on the meaning of “solid,” in the sense of “sound.” The term “sound money” is recognized in economics as a fixed definition of “healthy money.” “Sound money” is scarce, inflation-resistant, easily checked for authenticity, divisible, transportable, storable, and easily usable.