Those two icons mean that you are setup to receive e-mail notifications and flag notifications (in the forums) for that post. You can toggle that setting by clicking on either one of the images. The x will then disappear.
As of now, there is no way to do a category specific search. I believe some users have developed a workaround. Hopefully one of them will answer this thread
How do I subscribe to a thread without contributing adding a post?
Just click on the email notification button when it has no X. You can't flag a post you haven't responded to, although it will get an automatic red flag to show that you've read it. Instead of flagging it you can add it as a "favourite" or "bookmark" (the heart button) and it will show when you click on the "Show my favourite topics" button on the forum home page.