Green’s Dictionary of Slang

(US) one’s best clothes; thus those one wears to funerals.

1843		T. Haliburton Sam Slick in England II 37: If it warn’t for the black weepers and long faces of them that’s lost money by it.
1944		D. Burley Orig. Hbk of Harlem Jive 150: Weepers — Mourning garments.