[SippinLean]

It is [1]

> If you put a lower-case "x" to the right of a capital "E" (Ex) you can begin to see a hint of an arrow, though it is clumsy and extremely abstract. I thought that, if I could develop this concept of an "arrow" it could be promoted as a symbol for speed and precision, both FedEx communicative attributes. [...] Once I decided to refine the concept of the embedded arrow, I found that, to make the arrow more legitimate and identifiable, one needed to actually reconstruct the letterforms in order to make the arrow happen.

[1] http://www.thesneeze.com/secrets-of-the-fedex-logo/