Welcome Patrick!
I suppose a lot would have to do with the kind of signs you are wanting to make and the type of customers you are looking to attract.
I've done a few signs , but most of mine have been fairly simple, just letters and in most cases a cutout of the letters outlines. I've done a few that had some multi level carvings in them. For those I just used the plunge router with a spiral bit to do most of the waste removal, sometimes with multiple depths. Then used the wood carving chisels for the detail work.
I also built a CNC router table a few years back that I use for doing signs and other detail work on projects. Depending on your budget; familiarity with a computer and cad software; and shop space, these can be very useful.
Marketing depends on your target customers, but start with some examples of your work on a web page, selling on ebay (perhaps an ebay store), the yellow pages, and word of mouth. You might look into doing generic signs that might be popular (like the parking signs..."Harley Parking Only") and mass produced, or customized with a fill in the blank area.
Good luck, Post a little more info about yourself on the introduction forum when you get time. Hope to see some of your work soon.