An important element of a trademark application is a specimen showing the use of the mark in commerce where the mark would be perceived as a source indicator of the goods or services. One of the most common mistakes for Class 25 specimens is somebody will slap a logo on the front of a shirt and think that’s good enough. Wrong. That would be slapped down for being ornamental use.
Trademark ornamental use refers to the use of a trademark as a design element or decorative feature on a product, rather than as a means of indicating the source of the product. In other words, the trademark is being used purely for its aesthetic value, rather than to identify the product as coming from a specific manufacturer or source.
Here are some examples of accepted specimens for Class 25 clothing registrations:
For AIR ZOOM for shoes (Reg #6865381), Nike provided this screenshot from their online store:

For NOTHING LEFT BEHIND for jackets (Reg #6859769), Adidas provided these pictures of a hang tag with the mark on it:


Another common method is to use the clothing’s printed tag as a place for the trademark, like the printed tag on the neck of a t-shirt.
An important element of a trademark application is a specimen showing the use of the mark in commerce where the mark would be perceived as a source indicator of the goods or services.