With the World Series in full swing in North Texas, you know the "knock-off"/trademark infringing items are not far behind. To know if your t-shirt, cap or pennant is authorized by Major League Baseball check for a hologram sticker or holographic hang tag with raised-looking red baseball stitching. It may also have a sewn-in label or screen-printed notice identifying an approved licensee.
Be aware that many of the "tents" that pop-up along the street or in gas station parking lots are not selling the "real" thing.
The nice thing for the owners of federally registered trademark is the election between remedies under federal and state civil laws, and also state criminal laws. The Texas state civil trademark infringement law is located in Title 2 Section 16.26 of the Texas Business & Commerce Code. The criminal trademark counterfeiting statute is found in Texas Penal Code Section 32.23.
You might also want to keep your eye out for fake World Series tickets. Five folks have been arrested for selling fake tickets in North Texas.