So, SCO tried to trademark the mark “UNIX SYSTEMS LABORATORIES” (originated by AT&T) back in June 2004, and that has now been rejected (subject to appeal) by the USPTO. You can see all the documents on the case on the USPTO page for US serial number 78438912
The following summarises the reason for rejection, with my emphasis on the word “again”.
Registration of the proposed mark is refused again because of a likelihood of confusion with the marks in the following U.S. Registration Nos.: 1390593, 1392203, and 2241666. Trademark Act Section 2(d), 15 U.S.C. §1052(d); TMEP §§1207.01 et seq. […]
In this case, Applicant’s mark and the Registered marks all share an identical term, UNIX. The term “UNIX” is the dominant feature of the marks. The mere addition of a term to a registered mark does not obviate the similarity between the marks nor does it overcome a likelihood of confusion under Section 2(d). [….]
Therefore, the presence of the highly descriptive wording, “SYSTEM LABORATORIES,” in the Applicant’s mark is insufficient to overcome the likelihood of confusion. In re E. I. DuPont de Nemours & Co., 476 F.2d 1357, 177 USPQ 563 (C.C.P.A. 1973). The average purchaser of the goods or services is likely to believe that Applicant’s goods or services emanate from the same source as the goods and services under the registered “UNIX” marks. Additionally, Applicant concedes that the marks are substantially similar. Since similarity in any one of these elements is sufficient to find a likelihood of confusion, the marks are confusingly similar.