During my recent short holiday in the Netherlands, I spent one day visiting with old colleagues. Which was great fun of course! But I had left a bit earlier, so I could take photos of the tulips and blooming apple trees. And then I came across this. A blue and white pole with a red/orange plane on top.
I have posted something similar several years ago, but with ships on top. Here's the link. And basically it's the same as with the ships, except with planes. Now, I saw two of those plane poles, but there are several more. Because during WWII several planes didn't make it back for whatever reason and 'landed' in the NOP in the Netherlands. And since that area had only just become sea-free (1942), they were easily visible.