These hat hook/tie clasps have been around a long time and I've kept one a baseball cap off/on over they years, but as for being worn for 'good luck', I can't say they've helped me catch any fish.
They fit snugly on a baseball cap bill, but the brim on my boonie hat is a bit thinner, so this one needed something to tighten it's grip to better secure it. Bending the hook any further isn't an option, having already tried that with some pliers, so I added a two bight Turk's head knot with some 0.9mm cord to dress it up a little and keep it in place.
The gold plated Eagle Claw hat hooks are probably the most popular, but I preferred a more subdued gunmetal finish for the ones I currently use. They can also be found in other colors, like red, white, blue, orange, pink, and I've even seen a camouflaged version(ebay).
I was going to try doing my initials in Morse code on the hook, using thin and wide Turk's head knots/Spanish ring knots, but my initials would comprise a bunch of 'dots' and only one 'dash', so that'll probably be something for another project... I saw that idea mentioned on the IGKT forums, and member 'peejay' showed an example done on a cane, on the KHWW forums.