That picture above, looks so simple, it is the trail marker for GR routes in Spain, and I assume in much of Europe. A GR is a hiking route of 'gran recorregut' as in it goes a very very very long way.
I have walked a fair distance along a variety of these GRs, but they are sign posted with this very simple mark, often painted on stones. If you are going into a turn off you shouldn't be taking they take the two lines and make an X of them.
Clear and simple.
What has happened for me, however, is that I find I have developed a remarkable affection for these signs. The very long walk I did several weeks ago was marked with these, and when marching along in the dark on your own, these signs are MOST welcome.
So, a picture and a post, for two little marks, that are so very reassuring.