Casting tools I am thinking are probably small pieces of stonework that he puzzles together like one of these
but in marble. He puts them together to remember the steps of the spell, sometimes using his mystery to move parts through each other.
As to the sigil, I am not sure. My first thought is the sound of chisels working on stone, but that seems terribly uninteresting and predictable. I know I am already a bit basic so I want to think of something interesting.