John, if you notice in the first episode of series 6 everyone knew they saw something they just couldn't describe it. As we have learned before in previous series about perception filters, a filter to where you know you have seen something, but you just can't seem to remember it. The Silence seem to have that ability as part of their DNA or is psychic defense. It is not that the complete memory is erased just the ability to describe them or remember where you saw them. So the marks were to make note of how many they saw and that they saw them as a way of "counting" how many there were. I know what cliffhangers you are referring to, however if you know how this show works more and more will be revealed along the way until the finale. As for the Doctors final remarks about the Silence and the girl. He was being sarcastic and that is how the Doctor is, well for as long as I have been watching (since Christopher Eccleston) So he was really saying lets go and find out the who, what, where, why, and when.
Review of Day of the Moon
