SuperMan is cool... I dont have a problem with it... But I think that trying to wear clothing which attracts attention is not suited for certain situations.
If it's an emblem on the inside of a coat, I doubt anyone but him or his close friends or wife and kids will see it.
I think it is equally clownish for a hasidic guy to have a "superman themed cloak" as it is for a secular "dude" to wear a superman themed outfit. At the same time, I don't think its really such a big deal?