To signify, indicate, make known, can be done in various ways, by mouth (most commonly) by signs (the deaf and dumb) by showing, in revelations case (visions)
Some take that as an excuse to make any scripture say something else, but it's clear to some what scriptures are literal and what are synbolic or figurative, which also point to a literal meaning, and is often revealed in near by verses.
example "out of the sea" means out of the nations.
"the whore of babylon" is a religious identity, they are easy to assertain.
But heaven and earth being people in verses that are clearly saying about people, is just one little example of changing the meaning of scripture.