No. The best you can kinda do is notice that the text color changes when you've clicked on a link. So if the text color is the "clicked on" color, you know you've already at least looked at it, or done it.
You can also change the color code if you think you'd like a different color
as far as no hits available.. just because one click says they are not available doesn't mean that you cannot catch them.
each hit is [typically] just one of a specific quantity of tasks that the requester has released.
when someone else returns theirs, or it expires, it gets released back into the pool, and can be snatched up.
for this reason, you might consider using pandacrazy or hitcatcher or turkmaster to catch it.
be warned, though, the more things you have being actively sought, the more time in between each one's search