White stone
Archimandrite Nikifor’s Biblical Encyclopedia
(Rev 2:17) - many commentators connect the phrase with an ancient judicial custom: those favoring an accused person cast a white ball into an urn, while those judging him guilty cast a black one; a majority of white balls meant acquittal. Others see an allusion to white stones awarded to victors in the Olympic games, inscribed with their names and the value of the prize. Still others understand the golden plate upon the high priest's forehead, inscribed with the divine name.