The word Borg itself I do not believe is trademarked.
I didn't think you could trademark someone's last name?
https://en.wikipedia.org/wiki/Bj%C3%B6rn_Borg
A search of borg in the patent office shows the name used a lot: http://tmsearch.uspto.gov/bin/showfield?f=toc&state=4806%3Av...