Why Is America Dotted with Giant, Concrete Arrows?

[Petiver]

http://www.citylab.com/work/2015/02/why-is-america-dotted-with-giant-concrete-arrows/385472

[fennecfoxen]

Parts of America are also dotted with giant concrete Christmas-tree icons, but the aviation involved with those is a little less benign.

http://en.wikipedia.org/wiki/Christmas_tree_(aviation)

[hoopism]

https://news.ycombinator.com/item?id=6453401

Previous discussion

[shirro]

I like that in old Superman comics he would use one of these giant arrows as a key to the fortress of solitude. Only someone with super strength could gain entry.

At the time I first read a reprint of an old Superman with the aircraft arrow they had probably been obsolete for decades, which like English police boxes just seems to make them more magical.