Dagaz?

The Dagaz symbol smudged on the outside of my windscreen

I wrote about buying a rune set in this recent blog-post -
Well, Speak of the Devil, More Lizards?

And I couldn't help noticing that Dagaz symbol in my book that came with the set, as some prick has been marking my car's windscreen in the top left-hand corner for the last few years.
I usually notice it there when I drive out of a private carpark, like a shopping centre, or cinema.
I'll wash it off and then in a few months it's back again in the left-hand corner of my windscreen.
I'm sure it's not meant to represent the rune Dagaz, but I'm stumped as to just what it means and why some jerk keeps marking my car with that symbol.

The book that came with the rune set I bought

I know it's nobody from the unit complex in which I live, because I always park my car in my locked garage.
I'm sure I can't be the only one who has seen this mark on their windshield, but after doing net searches to find out why this keeps happening, I come up empty.

Maybe someone is just wishing me luck?
Or maybe I'm being stalked by an ex-co-worker from a certain Swedish furniture store that I used to work for?-)
At least it's not a set of crossed allen keys drawn on my windscreen;-)