Signs are an essential business. You can always branch out into other areas of graphics and advertising too. I would think wherever you go, there are shops that do really really well, and those that don't. It will depend a lot on how adaptable you are. Anyone on here that tells you their market is hot has the local formula worked out, and those that say their market is cold simply don't.
There are billions of dollars in signs and print sold every week in this country, you just have to figure out what your contribution will be.
One thing you could do would be to explore a market you are considering. Use Google and make some calls to figure out who the dominant player is in that town. Then decide if you do business in a similar way. If you do then great, and if you don't, chances are there's a market to be had taking the exact opposite approach they take.