[Bob434]

my guess is an old drug dealer marker for airplanes to dump their cargo

[Fungi]

You can do better than that. That is suppose to be facetious?

[dljordan]

“my guess is an old drug dealer marker for airplanes to dump their cargo”

No, it’s to guide mail and passenger planes before electronic navigation. They used to put the names of cities and towns on roofs too.