How funny you bring this up, I was just thinking this very thought last night. I would love to have a memento of sorts from my therapist. Maybe a photo of him that I take in his office? Or a nice hand written note from him? Maybe an object in his room that reminds him of me?
I've never asked, and mostly like will not. I sense that is crossing some boundary, though I'm sure I've crossed many in the time I've seen him!