A hidden sign in the safe house

[sampathkumarpsk]

When I was scanning through with the special flash light, I saw this in the safe house. What is this guys? It says 3 CIA and a right arrow

https://imgur.com/r98flGu

View: https://imgur.com/r98flGu

 

[ODark30]

It is part of the code required to solve the piano puzzle which reveals something new if I am looking at the image properly. I also dont think that is CIA but it does look that way though.