Fame
With so much competition out there—heck, even your Great Auntie Mildred paints watercolor portraits of Reagan in the attic all day—it's tough to get famous as an artist. Tough, but not impossible. Any time you have a special talent—especially one that creates a product—there will be opportunities for people to notice.
And who knows? Maybe one of those people will be an eccentric billionaire looking to wallpaper his mansion with professional drawings of his toupee.
If you choose the more typical route ("typical," in so much as you can actually afford to sketch for a living) and work with the justice system as a police sketch artist, you'll have a few opportunities to be seen and recognized as well.
When a manhunt is underway, you might see one of your sketches on the evening news or posted around town as a flier. Some might argue that you're actually making the murderer famous, not yourself, but you take what you can get.