The reference to "stone knee buckles set in silver" found below set me a-Googling. The only hits I got for the full phrase were for two theft cases from the Proceedings of the Old Bailey, London, dated 1766 and 1772. Knee buckles in general were a common adornment, used to secure the kneeband of breeches.
The Herald of Freedom May 20, 1791
Fifty Dollars Reward.
Last night the HOUSE of the Subscriber was broken open, and the following articles Stolen, viz.
A large Gold WATCH, with Gold Face, a Stone Seal with arms, set in Gold, a Silver WATCH, Silver Soup Spoon, a pair of Sugar Tongs and 12 Tea Spoons, and 1 Table Spoon, marked with a Cypher A. D. A Large Silver Tobacco Box, with arms on the top, a Silver Cross (or Stand) for the middle of a table, with arms, 2 Table Spoons marked H. D. a small Silver Funnel with a strainer, an oval Plated Tea Pot, a Plated Punch Ladle fluted, a pair of Stone Knee Buckles set in Silver, &c. &c.
Whoever will apprehend the Thief or Thieves, so that he or they may be brought to Justice, shall receive the above reward from me the Subscriber.
Roxbury, Jamaica Plain, May 19, 1791.