So imagine if our creators decided that a certain level of technological advancement was required before we could discover that we are not actually real.

That could look like a symbol, sign or something clearly un-natural:

• on something very small (requiring advanced magnification)
• on something out in space
• at the bottom of the ocean (which we still find very hard to get to, and dark!)

And it could be in multitudes, or just one instance, the latter meaning we would need to be full scanning and mapping and analysing everything.

Scanning sea-floors could be great for archaeology as well, given that a lot of land has been submerged since we became a modern species. Telling the difference between what was made by us, or our creators would be hard, so I only expect such an Easter Egg to be at the bottom of the deepest parts of our oceans.

They could make it doubly tricky, like only somewhere remote, and you need to use a scanning electron microscope to see it…