Glad you figured out the other things you wnated
and you should be getting a pop up alert on your board too-it is network wide-if I sent you a PM right now and you're on your board-after your next page load finished the PM pop up would appear. Sometimes image hosts are slow and the alert is only popping up when the pages actually finish loading so if you go to a link on the board before the page finished loading it won't be able to pop up for you.
As for images in signatures you bet you can!
You need to use BbCode though since HTML is not allowed in signatures. For example:
That will give you a image hyperlinked to your desired URL.