This shirt is likely a 2010 or 2011 design, and is variation on another seen among these USA Sonic Clothing pages. This one is all sepia tone, on brown tee. It says "Old School" in a somewhat 1970s styled font, with classic running Sonic stock art on arch/stripes. This seems to be meant to give it a look a bit older than Sonic actually is, but thankfully it does not use the 'fake wear' to the design. Note the "Top Heavy" tag in the collar.

 Discovered by Taaron

This is a simple & normal looking tee...except for the fact that the whole thing is pink. It is classicly styled, with a large Sonic right on the edge, which is a nice bit of design/helps make it stand out. The logo is on the sleeve, which is another nice touch. This is likely to be a Zara exclusive www.zara.com , which is a clothing store. Available in 2012. 

Is this a pajama or just a regular clothing set? It is labeled as a "Sport Set" but since it's soft cloth it could probably be used for both. It has a red top with blue borders that has a nicely shaded neo-classic Sonic jumping, his name in a new font, some stars and "Speed Player" written at the bottom. The shorts are blue with red trim, but don't appear to have any Sonic features on them. This set is from WalMart, and comes in kid sizes from XSmall through Large. Info added by SonicExia

This is a men's size tee that's fairly plain & simple. It's mottled gray, with simple red Sonic logo. It uses the old 'getting ready to run' classic Sonic stock art and then attempts to 'decorate' the shirt with little starburst shapes that have sound effects written in them like "Brang, Bloop & Bang". Why?
Sonic was never really associated with being super noisy, or being able to spell out his distinctive sounds. (Getting a ring, etc) Plus, did anything ever actually go "Bloop" in any of his games? It just seems sort of out of place on a shirt. Where is this shirt sold? How much is it? It's an ok shirt if you don't have several similar ones already.