These are spread all over the place, approximately every 5 m.
Survey whiskers! They're pretty commonly used to mark buried utilities, sightlines, possible expansions, etc. It looks like this one has been gone over with a mower. They last a really long time compared to stakes or poles (in that they can't be easily knocked down), are much faster to install and are often easier to spot in low/medium-low grass and brush than flags or spray marking.
