I live in a region where lots of people refer to most colas as "coke", but you bet if I start selling cola in a red can with "Coke" on it I'm going to have some lawyers showing up at my door.
This. I don't think that "coke" on its own can be trademarked because it's an actual common word (a form of coal). The trademark would have to be the word in combination with other aspects that make it distinctive. The color scheme, or font, or associated decorative elements, for instance.
"Coca-Cola", however, is distinctive on its own and is trademarkable as such.
> I don't think that "coke" on its own can be trademarked because it's an actual common word (a form of coal).
That wouldn’t be relevant unless you were actually talking about the form of coal.
Although many people say in shorthand that "[word] is trademarked.", trademarks are not “on a word” they’re on a particular use of a word. “coke” when referring to a beverage is mostly not a generic word. (Except maybe in the southern US :) )
For example "Apple" is trademarked in reference to computer hardware/software, etc. It isn't in reference to the fruit.
Trademarks are all about context. Exxon used to have a cartoon tiger as a mascot who sometimes looked a bit like Tony the Tiger. This was usually fine because the contexts were pretty different, one was for foods and one was for gasoline, radically different product markets. However, once Exxon started using their cartoon tiger mascot to sell the foods in the TigerMart convenience stores Kellog sued them and won.
If I go to a restaurant and ask for "Coke" they're not going to get confused and grab me some coal. I'd be pretty confused to open a red 12oz can that says Coke on it and find it full of coal dust. Nobody is confusing these products.
"Coca-Cola", however, is distinctive on its own and is trademarkable as such.