Check the logo. Ralph Lauren often contain a small stitched on graphic of a polo player riding a horse. On a fake Ralph Lauren, the mallet the rider holds will be more circular than rectangular. The tail will be difficult to see and the horse's right back leg will be bent. On a genuine product, the horse's tail is clearly visible and the right back leg is straight. You should also be able to clearly see the outline of the rider's leg. On replicas, the leg often lacks definition. As differences can be very subtle, it helps to look up an image of the actual logo for comparison. You may also want to use something like a magnifying glass to get a very close look at the Ralph Lauren logo on your product.

Examine the stitching. Turn your t-shirt inside out and examine the stitching on the bottom. A genuine Ralph Lauren should have one thin line of even stitching running along the bottom of the shirt. No stitching, or jagged and uneven stitching, indicates your product is fake.