Here's a pic G, they're quite different from the arrows: http://4.bp.blogspot.com/-vWLQ0sESDWg/TdF9HXoMfWI/AAAAAAAAA44/A9UGLcfhHl0/s1600/Early+Ogham%253F.JPG
Some bifurcating marks were also found next to cup marks in Cumbria 18months ago, and one of the outliers at Castlerigg also has similar marks, but are believed to be plough.