What happens if i marked something as spam on facebook?

I clicked on notifications and was going through them when i accidentally marked something as spam. the thing i marked as spam was a notification that said someone "liked" my status. What does marking them as spam do? Can they see that I marked them as spam? If they can see that i marked them as spam, is there a way to undo the marked as spam action?What happens if i marked something as spam on facebook?
No way to undo it. Facebook will check it out and if it's spam, remove it, if it's not, nothing happens.