If the simulators open a dialog with the simulatees?

That's part of was what I was alluding to by "... would we ever know?"

For example: let's say that which we call the universe is a simulation, and one (or more) of the entities running the project wants to communicate with one or more of the simulated personalities. How do they do it?

One option: adopt an 'avatar' in the sim. Now, think about where we get the word avatar in the first place....

Another option: the disembodied voice. Now think about how we categorize people who hear voices, on a continuum from Joan of Arc to Son of Sam...

A third option: neither an avatar or a fully-disembodied voice, but a compromise -- something on the order of a holy place where a sim finds a special transcendence, with perhaps some peculiar physical manifestation to guide him/her there. Can you say, "burning bush"? How about "Delphi"?

A fourth option: select sims (by whatever criteria, or none at all) and temporarily transfer their personalities to another (cyber)environment for study, questioning, instruction, whathaveyou. "Paging Whitley Strieber..."

From within our own context, the hundreds of examples of "visitation" recorded in all of the planet's cultures don't serve to prove that we are a simulation, any more than they prove the existence of deity... but they could just as easily be taken as articles of faith in simulation as they have been for faith in God(s).

To break through our cultural responses to the entire category of manifestations, it would have to be a global event, simultaneously experienced by every human, probably accompanied by a physical demonstration of unmistakable character or magnitude... but hey, we've already had those Revelations, too.