During the Arrow episode "Seeing Red" (S02E20) Moira Queen tells her son Oliver that she knows about him being Arrow, which came as quite a surprise to Ollie, but to me as well:
Moira: Oliver, I know. I know...I've known since last year, I suppose. In the night of the undertaking everything became so clear. It was pretty much the night I stopped sleeping.
Oliver: Before you say anything else...
Moira: There's nothing else to say, nothing I need to say...Except I could not be more proud.
But right now, I'm not sure if this was really a total surprise for the audience there or if it actually could have been known to us already that she knows about Arrow. While I don't think it was completely made clear earlier (since I think they would just have made more out of it during all the previous season 2 episodes), it might still have been alluded to in a slight way, to make you at least wonder if she might not know it. But currently I don't have too much recollection of the end of season 1 or the earlier season 2 episodes (and from her dialogue it seems she knew it as soon as the season 1 finale).
So were there any scenes in any earlier episode to either hint or downright clarify that Moira Queen knows about Arrow's identity or was this really a total surprise in this scene when she told him (which could imply it was quite a short term writing decision as part of "concluding" her character)?