Results of searching the USPTO database:

1. 2096022 -- UNIX  
2. 2039887 -- UNIX DIAPERS BY PANNOLINI  
3. 1988510 -- UNIXTRACS  
4. 1845474 -- UNIXWARE  
5. 1780785 -- UNIX SYSTEM LABORATORIES  
6. 1392203 -- UNIX  
7. 1390593 -- UNIX
Number 6 seems to be the relevant one:
Word Mark UNIX  
Owner Name (REGISTRANT) AMERICAN TELEPHONE AND 
           TELEGRAPH COMPANY  
Owner Address 550 MADISON AVENUE 
              NEW YORK NEW YORK 10022
              CORPORATION NEW YORK  
Owner Name (LAST LISTED OWNER) UNIX SYSTEM LABORATORIES, INC.  
Owner Address 295 NORTH MAPLE AVENUE 
              BASKING RIDGE NEW JERSEY 07920 
              CORPORATION DELAWARE  
Attorney of Record FRANK L. POLITANO  
Serial Number 73-544900  
Registration Number 1392203  
Filing Date 06/24/1985  
Registration Date 05/06/1986  
Mark Drawing Code (1) TYPED DRAWING  
Register PRINCIPAL  
Published for Opposition 10/29/1985  
Affidavits SECT 15.; SECT 8 (6-YR)  
Type of Mark TRADEMARK  
--------------------
International Class 009  
Goods and Services COMPUTER PROGRAMS;
  DATE OF FIRST USE: 1972.12.14; 
  DATE OF FIRST USE IN COMMERCE: 1972.12.14  
--------------------
This would appear to imply that the trademark was first registered by AT&T, and is now in the hands of UNIX System Laboratories.

UNIX was first registered by AT&T, however, it is now held in trust for the community by The Open Group. The correct attribution for UNIX is "UNIX is a registered trademark of The Open Group." See http://www.opengroup.org/trademarks.htm and http://www.unix-systems.org/trademark.html for further corroborating evidence.

More fun with trademarks from TESS, the USPTO's trademark search engine:

UNIX®

  • Trademark 75732193: UNIX "storage and transportation of high compressed gas, metal storage tanks for preservation, and manually operated metal valves. FIRST USE: 19990311. FIRST USE IN COMMERCE: 19990311"
  • Trademark 75079172: UNIX "opthalmic frames; sunglasses; and, parts thereof. FIRST USE: 19960606. FIRST USE IN COMMERCE: 19960606"
  • Trademark 74713724: UNIX DIAPERS BY PANNOLINI "disposable diapers. FIRST USE: 19950131. FIRST USE IN COMMERCE: 19950731". Drypers has since bought Pannolini.
  • Abandoned trademark 73698917: UNIX "WRITING AND DRAWING INSTRUMENTS - NAMELY, FOUNTAIN PENS AND BALLPOINT PENS"
  • Abandoned trademark 74306860: UNIX "golf shafts"
  • Trademark 73544900: UNIX "COMPUTER PROGRAMS. FIRST USE: 19721214. FIRST USE IN COMMERCE: 19721214" registered by AT&T transferred to UNIX SYSTEM LABORATORIES, INC (apparently a unit of The Open Group)

Read More: http://cm.bell-labs.com/cm/cs/who/dmr/otherunix.html

LINUX®

  • Trademark 75735641: LINUX "laundry detergents and laundry bleaches for home use; all purpose cleaning preparations for home use; general purpose scouring powders; skin soap for personal use; perfume; essential oils for personal use; preparations for personal hygiene and cosmetic purposes, namely, hair shampoo, skin toners, shower gel, skin lotions; hair tonic and toothpaste"
  • Trademarks 75867400, 75867401, and 75868269: LINUX "SALE SERVICE, IMPORT AND EXPORT, BIDDING AGENT FOR VAUIOUS PRODUCTS FROM DOMESTIC FACTORIES, PRICE OFFERING AGENT FOR VARIOUS PRODUCTS FROM DOMESTIC AND INTERNATIONAL FACTORIES," "COMPUTER PROGRAMS, DATA PROCESSING," and "DISKETTE, CD-ROM, CARD READER, HARD DISK, RAM, CPU, ROM, MICRO-COMPUTER, SERVER COMPUTER, DATA PROCESSOR, SOFTWARE, PROGRAM, DISK DRIVER, DATA READER, TAPE WITH PROGRAM, DISK WITH PROGRAM"
  • Trademark 75815006: MS-LINUX "computer software for desktop, client and server applications for computer systems and computer peripherals including internet applications". At least it isn't registered to Microsoft.
  • Trademark : LINUX "computer operating system software to facilitate computer use and operation. FIRST USE: 19940802. FIRST USE IN COMMERCE: 19940802" registered by Croce, William R. Della, Jr assigned to TORVALDS, LINUS

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