The OK K.O.! 2017 SDCC T-Shirt was the only "official" OK K.O.! Let's Be Heroes merchandise from the Cartoon Network online merchandise shop before the Cartoon Network shop closed down in early 2021. It was only available for a limited time in 2017.
It is a blue t-shirt that had a logo design of K.O. in the show's triangular logo design with the tagline "Let's Be Heroes!". It had the "SDCC 2017" tag under to represent the show's promotion from the San Diego Comic-Con event.