Crossfield does it(or did some time in the past) but strange that a tour pro does it as he has a caddy.
He probably just has them on while he learns them. Also just to show off his pro yardages. No harm in that.
I am sure I've seen other pros doing it so nothing wrong with it. If his girlfriend is merely a bag carrier it makes sense for him to have something written although surely she could have them in all the caddy notes they seem to carry even if Westwood is doing the maths on each shot