I have read that it's a sign of Hashi's. Because it's the periodic hyper levels that somehow cause the ends of the fingers to swell and the half-moons disappear. I didn't understand it at the time and I still don't. But if that were true, all people with Graves' would be missing their half-moons, and I don't think they do.
Anyway, mine are all missing except on the thumbs. And they haven't come back even though I've been optimal for years.
It isn't that it is a major issue in itself. It is that the issue is found alongside several disorders including chronic kidney disease, heart disease, as well as thyroid and B12 - and probably many other disorders/diseases.
Here's a quick search to give you a few things to worry about.
(Obviously, that is just me trying to lighten the tone with some flippancy.)
Content on HealthUnlocked does not replace the relationship between you and doctors or other healthcare professionals nor the advice you receive from them.
Never delay seeking advice or dialling emergency services because of something that you have read on HealthUnlocked.