Welcome Mike. There are some real derelicts on Ebay these last few years. Some of them are making fake porcelain signs that are even seasoned collectors can find difficult to discern authenticity. Especially just from a picture. It can be fun to buy online but if you end finding out you bought fakes at or close to original prices, and you have a conscience-it will be hell for you when its time to move them on. I think the best place when your new to get an education is by attending quality antique advertising shows.
Again, welcome, and good luck on your quest.