What is the inference

[KARL]

...when somebody says he does not trust those who do not have "halfmoons on their fingernails". I came across this recently, presumably referring to the light coloured arc at the root of a nail, but nobody has been able to explain what its absence is meant to imply (undesirable, one assumes).

[electrokitty]

I don't know about undesirable, I was always told that no half moons is an indication of bad health, particularly high blood pressure.