When I post something on FB, more than 'Like' I want to know who's gone through the words or seen the image I've posted. Many friends/visitors who go through the posts/see the images, might want to convey just that, instead of necessarily 'Like'ing it. In the absence of a means to convey they have done (read/viewed) so, they have no choice but to log a 'Like'.
Page-managers on FB do get data about the reach of their posts. But 'reach' is not the same as 'gone through' or 'seen'.
For such a phenomenon, I sense there should be 'Acknowledge'. That, to my mind, will be a very very rich source of information for the person who is posting something important.