I think patch jackets slowly disappeared because of the changes in the participants and changes in attitudes. Just like Sam and Akimbo stated, patches transferred over from the military and many young and adventurous divers were ex military guys. Bravado and macho were something to be proud of then and not seen as immature, dangerous, or silly.
Nowdays with how politically correct everything has become and the whole fanatical world of safety, patch jackets would be seen as a symbol of some ignorant cowboy or macho diver out of touch with the sensibilities of the ocean and the reefs.
Instead, what I see now, at least where I am from, are back windows on pick up trucks plastered with all sorts of freedive and spearfishing stickers along with all sorts of manufacturer logo stickers of freediving and spearfishing equipment. That’s about the closest thing I see to symbolism these days.
There still is an element if macho and daring that exsists in freediving, but it’s not allowed anymore in scuba. Scuba has become very touchy feely butterflies and rainbows pretty fishies (sea kittens) and any sort of percieved testosterone driven ideology has been heavily frowned upon. Scuba is a family sport now with gentle men, wives, kids, grammas, etc.
On the other end, tech diving really downplays testosterone driven machismo and heavily recommends people examine exacly why they are motivated to tech dive before they even start. They are advised to proceed with a perfectly neutral attitude and pay close attention to their ego awareness level. Ego and macho have no place in diving anymore.