conspicuous by (one's) absence
Noticeably missing from something. You're the loudest one in the class, so of course you're conspicuous by your absence!
conspicuous by your/its absence
If someone or something is conspicuous by their absence, people notice that they are not there. He played no part in the game and was conspicuous by his absence at the post-match celebrations. Mathematics and science were conspicuous by their absence at the university.