Here are a few quick tips that will help you get the most out of the forum...
How to quickly see the latest posts:
Use the "Participated" button in the upper right corner of the page. It turns blue when any of the conversations you've joined have new posts.
Bookmark the "Recent Threads" link from the home page (http://thewriterspub.proboards.com/threads/recent). That link shows you all of threads with the most recent posts (including new threads).
In either of the thread lists above, click the blue "New" button to the left of the thread title rather than the link on the title itself. That button takes you straight to the first post you haven't seen yet (this feature is one of the most AWESOME things about ProBoards.)
ProBoards has a "thumbs up" icon for liking a post.
If someone has liked one of your posts, you'll see a bubble above the "Profile" item in the top menu with a number in it. Click the number, and you'll see a page of notifications that includes any likes you may have received.
I'll put something together. One of the disappointing things is that the signature box has a rather small limit on the number of characters you can insert into it. You can't get too fancy with BBCode or put in very many images because of that. Do you have any control over the size of signature code on the admin side?
It looks like you guys have mostly figured it out. Here's what I did for one of my book covers. Explaining how I did the rest of the signature would take a bit more doing...
[url=http://www.amazon.com/dp/B0070PJ810/][img height=125]http://ecx.images-amazon.com/images/I/51HzDArAabL._SL160_.jpg[/img][/url] To customize the above for your book, swap your Amazon ASIN for mine (B0070PJ810) and swap your image path for mine (http://ecx.images-amazon.com/images/I/51HzDArAabL._SL160_.jpg).
The cover image needs to be somewhere accessible on the web. You can sponge it from Amazon. As long as you are linking to Amazon for the sale, they shouldn't mind. (This is what the KB link maker does for you, FYI.) Here's one way to do that:
Search for your book on Amazon.
In the search results list, right-click over your book cover image and select "View Image Properties" (or your browser's equivalent) to get the URL of the image. You can usually copy it out of the dialog that appears.
The image will have goofy name like mine does above, and it will have a white-space border on the left and right sides. If you want to get rid of the border, change the end of the name from _AA160_.jpg to _SL160_jpg.