"New Stations: Special Land Stations", Radio Service Bulletin, April 1, 1920, page 5. The "8" in 8XI's call sign indicated that the station was located in the 8th Radio Inspection district, while the "X" signified that the station was operating under an Experimental license.
"New Stations: Special Land Stations", Radio Service Bulletin, November 1, 1921, page 3. The "Y" in 8YO's call sign indicated that the station was operating under a Technical and Training School license.