You're right - "un cheveu" is masculine, so the store's name should be Beaux Cheveux. beau(x) = masculine belle(s) = feminine bel = form to be used before masculine nouns beginning with a vowel/=mute h (e.g. un bel hôtel)

That sort of mistakes happen all the time, some borrow word because they are "pretty". Like Rihanna having "rebelle fleur" tattooed on her neck. The words are in the wrong order, silly really.