What does "subtle" mean as a single-word reply?

I am watching US Open these days on its website. There are advertisements by a company called "esurance", where a man showed to a woman a huge check and started to introduce "esurance", and then the woman replied "Subtle!", if I am right about what I heard.

I can understand some usage of subtle as part of a sentence. But I was wondering what "Subtle!" means as a reply generally?

In English, single-word replies often denote sarcasm. A common example you might often see in movies and TV is: if someone says a lame joke and someone else replies in an unenthusiastic tone of voice, "Hilarious," it implies that the person thinks that the joke was not funny at all.

In the case of your example, the lady was probably commenting on how unsubtle the man's advertising of Esurance was (modern commercials often enjoy poking fun at themselves in that meta way).

maybe short for: "that is subtle"

it maybe being used in the same way that someone says: "clever!"