This is one of those "Secret Recipe" kinda things; sounds not-so-good, but if you try it, you'll probably like it. I prefer an inch and a quarter Ribeye; once out of the fridge
, schmear plain ole everyday yellow mustard all over it; top, bottom, sides. Then let it set (covered) till it comes up to room temp. Throw it on the coals; cook as usual. The mustard will mostly disappear as the steak cooks; there will be a bit of brownish color left behind, but the flavor is "Oh so good"! Your own version of spices and seasonings can make it even better, but it will be fine without.
Once tried, you might even try other versions of mustard, just for fun.