This item is a sort of 'proto-prototype'.
It's a catalog card that's only intended for company consumption or display. It was created by Top Heavy Clothing to show the intention of a Knuckles Chaotix tee design they had in mind to make. The design alone is shown at left, how it would look on the tee is the center drawing & the Sonic modern logo at right, would likely appear elsewhere on the shirt. Note the water-mark. This shirt DID get made too! You can see it on USA Modern Clothing. It was well liked by fans for featuring the Chaotix & starring Knuckles. It is a fun and cool design for fans.