I checked Heitman (Historical Register and Dictionary) first. He calls it "Signal Corps" from its inception on p. 44, Vol. 1. On page 614, vol. 2, table 31 lists 14 2LT's in 1889 and 10 1LT's on 8 March 1898, p. 616 and 3 1 LT's on 26 April, 1898 p. 618.
I bet they used "USSC" to differentiate themselves from the volunteer signalmen raised for the war.
Have a picture of a SC officer who won the MOH in the Phillipines early in the 20th century.
A Company member has insignia from the "US Signal Service" from 1863 in his collection.
I knew I had heard of the "United States Signal Corps" someplace.
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