ni73z = nites = nights
The billboards and signs are:
Probably the MegaGamers bear as seen on Piro's shirt at the end of Chapter 5, though some swear it's Mr. Muffin
CoE = Cave of Evil, Miho's haunt
メガゲームズ = MegaGamers
EDS = Emotional Doll System, part of Ping's programming
Compudog, one of the places Erika bought computer parts from
レンタジラ = Rent-A-Zilla
TPCD Zilla logo from the MegaGear t-shirt

What, no Yuki?

Piro speaks:
actually, she is in there - very small, in front of Miho, but further away in the dark.
Not joking either, that's her. She's just really no where near close enough to be able to put in much detail (think a few mm tall in the original drawing :)