I would clean that off (lightly wire brush the rust off too) and use some Duplicolor engine enamel paint matte black. Why engine enamel you ask? Cause I've used the stuff on exterior and it is very strong and dries very fast.
Also...if you look from the back of the car the exhaust flange is rusty and ikky looking. I sprayed that as well. Basically I use this stuff when cleaning up partially rusted metal bits. (Also works great for plastic bits as well).
Another thing you can use is Rustoleum...but it takes longer to dry and I think most of them are semi-gloss/gloss finish.