Royal Society ordered that its coat of arms be engraved on the silver box holding Leeuwenhoek's diploma

February 29, 1680

According to Birch's The History of the Royal Society of London, (vol. IV p. 13), at the 19 / 29 February 1680 (O.S./N.S.) meeting:

Upon mention of Mr. Leeuwenhoeck's diploma, it was ordered, that the arms of the society be engraved on the silver box to be provided for the diploma.

The image on the right (click to enlarge) shows a detail from Verkolje's portrait of Leeuwenhoek. The silver box is clearly visible, but the Society's seal is not.