Do you drive past bushes and brush them? Can often cause what you're describing. From my previous experience anyway.
That was the first thought but then realised it's the drivers side. So unlikely! Washed and polished it on sat and they definitely weren't there then. Went out for a drive and positive they weren't there when I got back. All Sunday it sat on my drive. Monday I was out in it with the gf most of the day but it doesn't look like it happened by someone driving past as the mirror isn't touched and the scratches are below it.
Tuesday it was sat outside the house all day.