How to start an online sign business?

You need your own website. Facebook was just a way to put the site, not where the signals are sold itself. For your type of business, a website is important to promote a better understanding of your business. Treat it like your brochure online where people can see and learn about your business.

One suggestion

I suggest you look how FASTSIGNS, one of the leaders in this field, use your website for your business http://www.fastsigns.com/ ... Use your website to accept requests for quotes from customers. That can be your tool to show the types of signs that you can do, and they have done in the past.

Consider this

Having a website will allow you to market your business locally. See how your business can rank well in Google Maps. Create a Google account Places and be sure to link your site in there