Another uncommon but cool example of the "AR Enhanced Tee"
This very...bright yellow-green shirt is either a mens size, or a boys/teens size. It is by Dynasty Apparel (their first appearance here), and it is 'augmented reality' enhanced. See the sticker in the top corner? It explains how to 'use' the shirt with a smart phone. If you get the BoostAR app, you can use the phone's camera vision to look upon the design, and it may show animation / 3D graphic over the actual picture. *What does this actually do? Write in if you've tried it.
The flourescent color of the tee with the red, blue, green & black detailed designs makes this shirt a bit loud. This appears in 2015, but it is not common. Where is it sold?

This is a lycra-like material all-over print tee. The slogan here is "Sonic Rock The Speed", which is written at the bottom on the back of the shirt. The front has pointing up/jump Sonic while the back has jumping twist Sonic. The background is an abstract sky, desert mountains, and a somewhat abstracted runway pavement. This shirt is in mostly little kids sizes. XL may fit teens. This was a Sears 2014 item.

This black tee from Kohl's stores (usually if it's seen there, its generally exclusive to Kohls) brings something a little new to the table. Sure it's got a nice dynamic pose for CG Sonic for the art, but it also has a Red Star Ring, 10-Ring icon, 2 springs & the Green, Purple & Blue chaos emeralds along with a star bumper. It's cool to see the items from the game actually getting used as background graphics. Sonic's name is spelled out across the top, & the modern logo is at the bottom. Look at the paper tag. It is square with checkers & CG Sonic face. The back is blank except the letters "TMI" in a rectangle. This is in the boys/teens area of the store, in winter 2015.

 Discovered by Shadowfoxx757

Here's a shirt from winter 2015, at K-mart.
It's not to be confused with a different shirt, with the same slogan, from Wal-Mart. (That one is red, and has a different graphic) This tee is green, with "My Game Never Stops" written in a blocky white font. The Sonic graphic here is plain, un-shaded color art and overlaps the text. The modern logo is small & in color at the bottom. It's a boys/teens item. 

This tee is likely also available in red and white. This green one is little kids' sizes only. It's All Stars Racing Transformed, and is a Sears item. It is on clearance at the end of 2014. The notable thing is the sewn-on stripes on each sleeve. The red version of this may be the more common one.

This is a fun set, too bad it's just for toddlers.
This is the Step It Up 2 piece set with tee & matching shorts. The red tee has 3 rectangle portraits for Tails, Knuckles & snowboard-riding Sonic. All are CG, with small squares for the background. It says "Step it Up" in a thick font next to Tails' portrait. The shorts are primarily blue, with red thick lines up the edges. One leg has CG Sonic in a gold ring, with the modern logo below him. The waist is elastic.
This set appears in later 2015, but where is it sold?