Often on the grave stones of kohanim there is an engraving of two hands with fingers spread as kohanim do during birchas kohanim. (For an example drawn randomly from Google Images see here.) What does it mean if the thumbs of those hands are engraved broken?
(This appears on a gravestone in the United States of which I will post a picture if I can get one.)
In the Artscroll book, "Bircas Kohanim" by Avie Gold & Nosson Scherman (p 41) one of the various positions for the kohen's hands illustrated has the thumbs touching not at their tips but at the joint (knuckle). The tips of the thumbs are separated to give a space in between them. Could this have given the impression of the thumbs being broken?
Perhaps it was vandalized, perhaps the engraver did not do a good job, or maybe the Kohain was married to someone he was not supposed to marry and still wanted the Kohain hands and they intentionally made it with broken fingers to indicate that.