“Ἀποκάλυψις Ἰησοῦ Χριστοῦ ἣν ἔδωκεν αὐτῷ ὁ θεὸς δεῖξαι τοῖς δούλοις αὐτοῦ ἃ δεῖ γενέσθαι ἐν τάχει, καὶ ἐσήμανεν ἀποστείλας διὰ τοῦ ἀγγέλου αὐτοῦ τῷ δούλῷ αὐτοῦ Ἰωάννῃ.”
It is the unveiling (apocalypse) of Jesus Christ which God gave him to show to his servants the things which must soon take place, and he SHOWED BY SIGNS, sending his angel to his servant John.
He introduces the whole book using the verb σημαίνω, to signify, to make known by signs, etc. This of course comes from the word σημεῖον, sign, which John is fond of using. In his gospel, there are 7 such “signs” by Jesus.
The book of Revelation then is a collection of signs (not literalistic devices) to present the reality of God’s presence, love, comfort to his people, sovereignty, judgment to come, and deliverance to come – all of which are “revealed” because they stand somewhat hidden by the present reality of persecution and suffering.
Such revelation of the spiritual realities that underlie the temporary conditions of this present age is laced with and entirely derived from the Old Testament apocalyptic parables and signs. They all come together in a crescendo, in a much greater scale, as God now not only brings judgment and restoration to his people in the Ancient Near East, but also upon (eventually) the whole cosmos.
But this is all given through means of “signs” as he “signified” (ἐσήμανεν) what is to take place.
That verb is used in the New Testament only in 5 other places, 3 of which by John:
In John 12:33 Jesus indicates, signifies what kind of death he was to die, by a sort of a parable: “And I, when I am lifted up from the earth, will draw all people to myself.” The same happens in 18:32. Yet again in John 21:18 Jesus indicates by a parable or sign the kind of death Peter was to die: “when you are old, you will stretch out your hands, and another will dress you and carry you where you do not want to go.”
So one needs to be careful as one seeks to understand the Apocalypse. First, it is not a linear narrative (rather, it repeats several events from different points of view), and second, it is given by signification, not wooden literal devices.