From Cecil’s pile of knowledge (We Seesuls stick together. One lengthy explanation
Another theory for the US, at least is that it was like the letter “U” in colour, etc., a protest to the Brits after the Revolution.
I grew up by a major racetrack, even ate dinner this time last year at the turf club there, but never even noticed. The only thing I noticed was when my dad would declare: “the nags must be in” because the house was loaded with horseflies. We had this big red cake loaded with who knows what in the garage, where they would all meet their collective doom. As Sagan would say: “billions and billions of them”. G’nite AC
Keep on ponderin’ At least we’re on the right track here.