The main reason why big brand clothing buttons are engraved or printed with letters is for brand logo and decorative purposes.

These letters are the brand’s logo, just like T-shirts often have the brand’s logo or name on the front. Putting your own brand name on the buttons means that they are clothing accessories of the brand and also displays the brand's image. In this way, brands can increase the recognizability of their products and prevent consumers from confusing products from different brands.

In addition, these letters or words can also play a certain decorative role, adding beauty and personalization to the product. At the same time, for consumers, these letters or text also provide additional information, such as more details about the product or brand, helping them to better choose and understand the product.

I hope the above answers are helpful to you. You can check the official website for more information.