A bannered route or a route with multiple segments will have the first three letters of the associated place name at the end.
For routes with multiple segments, the longest segment will usually (but not always) lack the placename abbreviation. For example, vanilla NS4 vice NS4NGl et al, or ME113 vice ME113Fry and ME113Whi. Both NH ME113 segments (NH ME113Con & NH ME113Cha) have an abbrev.
In the case of NE59, the longer segment has the abbrev. and the shorter one none, as I didn't have anything good to name the shorter one after.
The first-three-letters rule is not always strictly adhered to: Fort Worth -> FtW, New Glasgow -> NGl, South Portland -> SPo, etc.