Also keep in mind that karma or reputation is different from clicking on "Like". To give karma you need to click on the star at the bottom left of the post, and then on the pop up, Approve or Disapprove and optionally give a reason.
Personally I add my name to the reason, so they know who it's from, but you don't need to. Also, I don't give bad karma or disapprove. I believe it to be counter productive, and really poor form.