Most likely
I.F in rectangle with crown (damaged) for
Johannes
Feddema, registered in Leeuwarden 1780-1825.
Below the same mark and contributed to Feddema c. 1790. NB. This mark
is not shown in Elias Voet book, Merken van Friese Zilversmeden, revised edition 1974 #529. Karel A. Citroen, Dutch Goldsmiths' and Silversmiths' Marks and Names prior to 1812, only mentions IF and IF crown.
Gratitude;
Mr. F. J. Haffmans