Many calls which are natural require an alert, and many that ARE NOT natural do not. So, "is it natural?" is a very poor test in any jurisdiction that I'm aware of. One of my favorite examples is that, at least in ACBLand, my 2♣ (playing a strong club system), which promises 6+ ♣ has to be alerted, but your "standard american" 2♣, which doesn't promise clubs at all, and can be just about whatever you define "strong" as, doesn't.