In fact this wording represents two words usually
written on many doors. Imagine this is a glass door. Reading every
second letter starting from the leftmost "P", you will see "PULL".
Reading every second letter in the backward direction starting from
the mirrored "P" at right, you will see mirrored "PUSH".
Nob Yoshigahara claimed he was inspired to this puzzle while visiting
a cafe and looking outside through its windows and doors.