It really is a hallmark of how good you are/have gotten as an artist/writer when you get people dedicating time and effort into making semi-decent porn of your characters.
Though when you think about it, that is a rather funny metric to rate the quality of one's artistic and/or writing abilities. It genuinely does act as a good measure for that, but it's still funny.

100% If I were to ever actually sit down, make something I love, and became a well established author/mangaka, the only true point I would recognize my popularity would be if people were drawing porn of my characters, only then would I realize I've been recognized in the eyes of the people