“That’s what I like about Texas” has been the slogan of Dairy Queen since 2003. A song jingle was created by Luminous Sound.
 
Songs such as “What I Like About Texas” by Gary P. Nunn and “That’s What I Like About Texas” by Dale Watson had both publicized the phrase by at least 1996.
         
A previous Dairy Queen ad campaign was “Texas Stop Sign.”
 
 
Luminous Sound
Luminous shines: this studio combines musical skills, new technology and an in-house ad agency - Audio Today & Tomorrow - Luminous Sound - Brief Article
Post,  August, 2002 by Christine Bunish
 
DALLAS—Luminous Sound’s clean and contemporary Studio Baurton designed facilities are a far cry from Paul Loomis’s spare bedroom where the company made its debut 18 years ago with an eight-track recorder and console. Many jingles later, the recording, audio post, commercial music and sound production studio offers its three top-of-the-line studios to an array of clients.
(...)
Earlier this year The Loomis Agency was awarded several new clients whose commercial audio needs are being met by Luminous. Loomis and Michael Tuggle, creative director at The Loomis Agency, penned “That’s What I Like About Texas” to pitch the Texas Dairy Queen account. The tune with a country flair accompanied a collage of images representing “everything cool about Texas,” Sizemore explains, At press time Loomis was crafting R&B, Hispanic, country and rock versions of the song. 
 
Google Books
Telling Stories, Writing Songs: An Album of Texas Songwriters
by Kathleen Hudson
Austin, TX: University of Texas Press
2001
Pg. 187:
The name Gary P. Nunn is synonymous with Texas music. He’s been an ambassador for the state with songs like “That’s What I Like about Texas.” “London Homesick Blues,” his signature song, is heard on the widely syndicated TV show, Austin City Limits. And at one time he was designated by the governor as the Lone Star State’s “official” spokesman.
     
Cowboy Lyrics
WHAT I LIKE ABOUT TEXAS
(As recorded by Jerry Jeff Walker & Gary P. Nunn)
(Viva Luckenback Album) (Key of B or G)
(...)
It’s another burrito, it’s a cold Lone Star in my hand!
It’s a quarter for the jukebox, boys,
Play some songs by your favorite Austin Texas band!
 
Yee-Hoo! That’s what I like about Texas! Yehaw!
 
Austin Chronicle
HOME: NOVEMBER 28, 2003: MUSIC
Texas Titles in Toto
Of the estimated 3,500 songs written about Texas and Texas Places, most of the votes came from one of these two lists below. 
(...)
“That’s What I Like About Texas,” Dale Watson  
 
(Trademark)
Word Mark THAT’S WHAT I LIKE ABOUT TEXAS
Goods and Services IC 043. US 100 101. G & S: Restaurant and carry-out services. FIRST USE: 20030100. FIRST USE IN COMMERCE: 20030100
Mark Drawing Code (1) TYPED DRAWING
Design Search Code
Serial Number 76444016
Filing Date August 27, 2002
Current Filing Basis 1A
Original Filing Basis 1B
Published for Opposition April 1, 2003
Registration Number 2807339
Registration Date January 20, 2004
Owner (REGISTRANT) TEXAS DIARY QUEEN OPERATORS’ COUNCIL CORPORATION TEXAS 2120 Forum Parkway Bedford TEXAS 76021
Attorney of Record MOLLY BUCK RICHARD
Type of Mark SERVICE MARK
Register PRINCIPAL
Live/Dead Indicator LIVE