Pretty much exactly what the description says. How subtle is a Subtle Spell? Is it covert enough that no one would know the sorcerer has used it? Is it literally no more than "the spell happens without somatic/verbal components," such that anyone can tell you still cast it?

I don't believe there are any "right" answers, though of course I have my preferred answers. This is more "how does this community feel about it" than anything else.