"Do not board"

As in a train.

It is generallly the placeholder, displayed in the city field, for the overhead signs at a large or central trainstation (Hauptbahnhof) when the train is at the platform, but the destination has not been designated.

Hence the saying "all the empty trains go to Nichteinsteigen"

The city of no would be "Neinstadt", formerly known as Bonn.

 

Klebnor

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.