Larry Hurtado summarizes a monograph on inscriptions in Roman Asia Minor that refer to "angels":
He says "A number of the inscriptions in question are in burial sites, and warn against disturbing the graves, effectively warning the ire of angels if anyone does so. They also come from a particular geographical area in present-day Turkey, and a few islands off/near the Turkish coast."
This, of course, intersects with the time and place of the apostle John's ministry. I wonder if that's applicable to John's enigmatic reference to "angels" in Rev 2-3. What does John mean by that appellation? Does he mean "angels" in the technical sense of the word? If so, in what respect do the churches have angels?
Keep in mind that the inscriptions are just a surviving sample. Presumably, there were more inscriptions of the same kind.
As I've noted before, I think the identity of the "angels" depends in part on whether we view Rev 2-3 as an interlude in the narrative, or part of the narrative. John's vision begins in 1:9. If Rev 2-3 are a continuation of his visionary experience, then it could well denote angels. To say the churches have angels within the visionary narrative doesn't imply that the historical churches of Asia Minor had angels. We need to distinguish what happens inside the visionary narrative from reality outside the visionary narrative. Things can happen in the vision that don't actually happen in real space and time. Rather, visionary events point to something analogous.
However, the inscriptions raise another issue. According to the epitaphs, the angels have a deterrent value, to ward off would-be grave-robbers. Avenging angels who will punish those who presume to desecrate the grave.
This raises the question of whether John (or God through John) is trading on the local connotations of angels. By analogy, the angels of the churches could be guardian angels. That doesn't necessarily mean the churches literally have guardian angels. Rather, that's a way to indicate divine protection of the churches.