I have recently moved to Aalborg in denmark and while riding my bike each morning I cycle past these large signs pointing out into the water. I assume they are for aircraft at the nearby millitary/civillian airport because of how large they are and how they point directly out into the water in a relatively calm stretch of water on the edge of the city so nobody could see them.
The signs are quite large, about 1-1.5m in diameter and the poles are about 6 or 7 meters tall
The one interesting thing that made me think maybe its not to do with the airport is how it's actually quite far away (and also not lined up even slightly with the runway). In fact, they are almost perpendicular to the runway, about 4km away across the water.
I'd love to hear your thoughts on the matter, and apologies in advance if they turn out to be some other kind of markings. I am very curious to know!