The President was 'conspicuous by his absence' at the peace talks. [=his absence was very noticeable; people had expected him to be there and noticed that he wasn't]
He was 'conspicuously' [='noticeably'] absent from the meeting.
There were a number of 'conspicuous' changes to the building.
(..) anything happen to him. I promise. What do you think? The old Forest road? Yeah, that might be the least conspicuous. Nobody steals a whale. But I'm tellin' you, the whale is gone. The trailer's out of there, (..)1993 Free Willy