You can either go on the bottom of the left hand side there is a link there for My Posts. You can take a look at posts that you have left in the past, it will update as soon as you change it. Or you can start a new post or start replying to a current post and instead of actually posting just click on preview on top next to the Compose tab.
Re: How can you preview your siggy when you make changes?
DS #1- Ares Christopher
DS #2- Taj Lee
DD #1 Alba Gray
Baby #4- coming in May
Thanks! That helped me out.