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.

Picture of two sign poles, one large white circle with small red circle and one white diamond with red border

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.

image of a map showing how the airport runway does not line up with the sign's location, 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!

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    $\begingroup$ My first thought would have had them as some kind of marine traffic/shipping signage rather than aviation related... not sure though! $\endgroup$ Commented Nov 11, 2017 at 23:09
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    $\begingroup$ I don't think it is aviation related. Note that it is apparently made of wood & unlighted. Also, its size is relatively small if it were to be observed from a flying aircraft. $\endgroup$
    – kevin
    Commented Nov 11, 2017 at 23:34

1 Answer 1


It's a maritime navigation aid. I'm fairly rusty, but I'm pretty sure it's a form of lead mark. When seen from the water, as you travel towards the mark, if you keep the diamond centred between the circled dots, it will have you travelling in a straight line down the centre/safest path of a channel.

It will normally be associated with a channel through shallow water, or a hazardous bend, or promontory, or breakwater, or a safe entrance or exit course for a harbour, or similar. Sometimes there may be a progression of such marks to enable zigzagging along an irregular waterway with a minimum of course changes.

  • $\begingroup$ Related at the end of the page, the same signals in red, and with roughly translated names: Directional aid lower/upper. $\endgroup$
    – mins
    Commented Nov 12, 2017 at 16:25

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