They are not calling out copyright they are calling out trademarking.
With references to the approved trademark filings with uspto.gov.

K> No three alphanumeric characters can be copyright protected. 



>>From a message by Silver Dragon about OT: Copy right an Acronym?:
>> Today Mac from Fen got a 15 page letter stating that USO is a copy
righted trademark of some other company. Understandable. Does anyone forsee
the same issue if I typed it correctly as an acronym?
>> like U.S.O? can people copy right acronyms? I mean there is a
U.S.O tennis tourny as well as golf.
K>  > Silver Dragon (Moderator U.S.O 2003)

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