The events triggered by the seventh trumpet as recorded in Revelation 11:15–19 occurred in heaven (Revelation 11:15, Revelation 11:19). John himself is in heaven as witness to these events (Revelation 4:1). The sign validating the declaration of Revelation 11:15 occurs in the same area—in the presence of divine witnesses.
1 And a great sign appeared in heaven: a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars.