This firm produced perfins from 1930 to 1961.
Here are some GE covers produced in that time:
Used 24 April 1939 to Camden, New Jersey, USA
GE perfin on 2¢ Gómez definitive (1930) - Scott 309, Edifil 252
Used 25 October 1940 to New York City, USA
GE perfin on 10¢ international airmail (1940) - Scott C5, Edifil 256
Used 17 March 1942 to New Britain, Connecticut, USA
GE perfin on 3¢ José de la Luz Caballero definitive (1940) - Scott 310, Edifil 253d
Used 8 August 1942 to Schenectady, New York, USA
GE perfin on 3¢ José de la Luz Caballero definitive (1940) - Scott 310, Edifil 253d
GE perfin on ½¢ Victory postal tax stamp (1942) - Scott RA5, Edifil 5
Used 4 August 1942(?) to Chicago, Illinois, USA
GE perfin on 10¢ airmail commerative (1940) - Scott C32, Edifil 342
GE perfin on ½¢ Victory postal tax stamp (1942) - Scott RA5, Edifil 5
Used 24 March 1944 to Chicago, Illinois, USA
GE perfin on 10¢ airmail definitive (1931) - Scott C13, Edifil 264
GE perfin on ½¢ Victory postal tax stamp (1942) - Scott RA5, Edifil 5
Used 11 January 1947 to Schenectady, New York, USA
GE perfin on 5¢ airmail definitive (1931) - Scott C12, Edifil 263
GE perfin on 3¢ Postage Stamp Centennial commemorative (1944) - Scott 393, Edifil 375
Used 14 January 1949 to Victor, New York, USA
GE perfin on three 3¢ José de la Luz Caballero definitives (1940) - Scott 310, Edifil 253d
In Cuba, General Electric was the only company that had perfins cancelled in four different cities.
And here are some of the stamps which have GE perfins: