I found it later on, of course. Outside 'my property'. What disturbs me, is the fact that it was touched by someone, who didn't have my permission. My sketchbook is my sketchbook. To be honest, I wouldn't be that bothered even if my journal would be found and read.
Sketchbook is different.
These sheets of paper are intended for my self-development only. These sheets of paper are something that I experiment on. I wouldn't be overjoyed if they did it, of course. But wouldn't be as bothered. So, yeah, anyway.