Monograms date back to Ancient Greece as a way to denote where currency was produced. The practice of monogramming eventually fell into the royal ruling classes of Europe, as they monogrammed everything from personal items to coins pressed while under their rule. Today, monograms are used to denote personal property and often used in wedding gifts. When a couple gets married, monogrammed gear is way to personalize a gift meant for the couple. Aside from towels and bathrobes, guys have been placing their initials on shirt pockets, collars, and even wrist cuffs. Rules for monogramming extend to where and how to arrange the initials, what initials should be used, what kind of script should be employed, etc.
As the royal rulers of Western civilization have historically been white, this practice's long and rich history reminds us that this wasn't just a practice of adding personalized touches, but used as a way to remind others of a person's position and power—literally worn on their sleeves.
Generally speaking, monogramming things as a gift is pretty risky (in the event that they don't like it) and having it done to your own gear looks more pompous than personalized.