My thanks to everyone who gave me a heads up about this advertising campaign on Facebook. "Cool Tee USA" is indeed ripping off my Miskatonic Antarctic expedition logo. The ad buy seems to have popped up last Monday as a "Limited Time" offer, but since then the clock has been regularly resetting as the owners shift the offer through hoodies, posters, etc.
As of yet I haven't heard back from the company, but I'm sure I'll be hearing a variation of the "we got it from some guy" story. If you'd like to purchase a legitimate t-shirt or hoodie you can get them through the Propnomicon store on Zazzle.