These icons do appear to be caused by the Navigraph data and there has been some existing discussion. You may wish to check the following topics for more:
I just recently subscribed to Navigraph and have seen many many airports now have that symbol next to them. They are just the stock airports, I haven’t done any mods to them.
As the legend shows, it stands for Third Party Content. In this case, I guess Navigraph is the Third Party and the Content they’re providing is behind-the-scenes data.
By the way, I’m really loving the features and functionality that Navigraph provides. Very very cool!
From Navigraph forums: MSFS World map - All airports marked as 3rd party - Navigraph Forums
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