They did exist in the Model A era (though they were double-sided in those days), so I think it's an "up to you option" if you're not going for points judging at a MARC / MAFCA sanctioned event.
Heck, there are even period photos of big trucks and tractor-trailer rigs sporting WWW tires all the way around !
I think they help increase the visibility of the car in traffic. I have always had them on my antique cars (mostly 1940's).
My Special Coupe came with a set, when they're bald, I will probably go with BW, for pocket-book reasons.
Unless points-judging applies to you, buy what your heart and pocket-book like.