If you're having trouble with your signature showing up with your posts after you are done editing it, there are a few things you can do.
If you want your signature to show in selected posts [not all of the time] then when you are making a post, Just checkmark the box next to "Attach signature (signatures can be changed in profile)". That will attach your signature.
If you want your signature to be attached to every post you make then go to your profile, select "Preferences" and scroll down until you see "Always attach my signature".
If you have anymore questions about signatures, feel free to ask.