I think the dirt ont he sign is too intense, and too splotchy.
If it's just been sitting around for a while, without rain or anything, it would have a pretty even coat of dirt:
If it's been beaten up, it'll have dirt, rust and scratches:
but that makes more sense for a construction sign or something of that sort.
If it's REALLY old, the pain would have started to fade, crack, chip, and then the metal would rust from the chips:
Notice a couple things in that last one. The sign has rivets or bolts holding it to the post, these usually rust first on old signs. Those bolts have directed any water that's hit the sign, causing drip marks (or often, rust-drip marks from the bolt itself). Also notice that if you want it to feel old/abandoned stickers and graffiti help a lot in selling that.
The post itself looks ok, but as someone else pointed out, it feels like it's floating off the concrete. Many smaller posts like that tend to be inserted in the concrete after it has set up. They drill a hole, shove the pole in, and then fill in some more concrete around the pole:
Also look at the weathering/dirt/water stains around these parking meters:
Think about reorganizing your scene. The light post might be on the corner, and the garbage can might be next to it, but why would a no parking sign be there? Wouldn't the curb around the corner just be red? Also with your current angle/setup the sign & light post line up and it's hard to tell what's going on there. I'd pull your camera back a bit,a nd move the no parking sign to the top side of the picture on the other street.
Anyway, hope that helps some.