File Extensions cannot be Trademark Protected in the US

Well-known US CAD company Autodesk Inc. holds, inter alia, pending “DWG” word mark application (No. 78 852 798) claiming “computer software for [...] creation and manipulation of engineering and design data, particularly adapted for engineering, architecture, manufacturing, building, and construction applications [...]; CAD software; computer software for animation, graphics and design modelling applications”. "DWG" is an acronym of the term “drawing” and used as a generic and merely descriptive term for Autodesk's CAD file format. As of June 22, 2008, this registration proceedings as well as a number of parallel DWG-related trademark applications of Autodesk were suspended by the USPTO due to the pending trademark cancellation petitions Autodesk had filed against Open Design Alliance (No. 92 047 002) and Dassault Systemes SolidWorks Corporation (No. 91 170 857), to confront the fact that Autodesk's competitors have increasingly used "DWG" in various forms for their own software product names, and in marketing campaigns aimed at Autodesk customers, whereas the final disposition of these proceedings could affect the registrability of Autodesk's DWG trademark. In the notice of suspension the USPTO notified Autodesk about the following concers that may oppose to the registration of the DWG word mark: DWG is a file format; Applicant is not the exclusive source of files with the format name DWG; Applicant does not control the use of DWG by others, either as a trademark or as a file format name; The submitted survey does not reflect recognition of DWG as a trademark, since no distinction was made between use as a trademark and use as the name of a file format. Later, on March 16, 2010 and May 21, 2010 two Letters of Protest were filed, both from the Office of the Deputy Commissioner for Trademark Examination Policy. Both protests have been found relevant and supporting a reasonable ground for refusal according to 15 U.S.C. § 1052 (e) (1), requiring that “merely descriptive or deceptively misdescriptive” trademarks shall be refused. With the letter of protest of March 16, 2010, extensive evidence (140 pages) has been submitted as to possible descriptiveness and/or genericness of the acronym “DWG” due to its functional use as file extension, based on the fact that file extensions are functional and that computers use them to identify formats, and associate them with application programs. It is a fundamental rule of trademarks that they are not issued on symbols or marks that are entirely functional. The letter of protest of May 21, 2010 relates to US case 3:08-cs-04397 (Autodesk vs DS SolidWorks) pending in the Northern District of California, in which Autodesk sued SolidWorks for acts of unfair competition including alleged infringement of Autodesk's “DWG” trademark due to SolidWorks' usage of the characters “DWG” as part of software product names, domain names and the like (cf. Document 1, Complaint, of Autodesk vs DS Solid Works, filed…