well in most games, the 4 character clan abbreviation is the clan support. As the organization on the forums and steam is so good when it comes to clans, i dont see the need for much more. if everyone in your group is not on your steam list your group is just way to massive to worry about imposters, or you are a really out of the loop member. (and if someone actually does try to fake being in a clan, which doesn't happen often at all because steam exists, good for your clan, you have gained enough fame that someone wants to copy you, or you have terrible members who were so antagonistic or annoying that someone now thinks its worth their time to try to lower your reputation)
i mean, i get it, comprehensive ingame support would be cool for all the "competitive" crowd, but in reality its a fluff feature (and the kind of fluff feature that targets people who wont stop playing the game, and have already set up everything that will be ingame through steam and the forums and private websites). once everything essential to the game is done, yeah it would be great. but until then, the tag is a great addition.