Although the zipper pull on a real COACH bag will be made of leather or a series of rings, the actual zipper mechanism which pulls the two sides of the zipper together should be embossed with the letters “YKK”. This is the highest-quality manufacturer of zippers and COACH uses this brand.
Sometimes it’s hard to see, especially on a photo. Even in person, you may need a magnifying glass to see the YKK, especially with very small zippers.
Note: I have never seen a regular zipper pull on a Coach bag – in my experience, they are either made of leather, a single ring, or series or rings. This is one of the wonderful ways Coach makes their products unique, down to the very smallest detail!
Many AAA quality fakes have YKK zippers too! However most authentic coach bags have the YKK zipper on the inside zip pocket and most of the fakes will use a cheap zipper inside the bag. (example, the authentic 11689 does not have YKK on the outside zipper, but most importantly it is engraved on the inside zipper)