We'll know that we've reached AGI when a key conservative political belief in the US is that AIs are not people and do not deserve rights.

We'll know that we've reached the singularity when there's a mysterious and superintelligent AI entity with technology and motivations that we as humanity do not understand and have no control over. Not sure why we want that, exactly, but that'll be the big sign.

That's the fun part. We don't. Could have happened 10 years ago without us noticing. I don't expect my skin cells to be able to recognize "me" anymore than I expect we will be able to recognize a superintelligent AGI. If it arrived 10 years ago, then the last 10 years could simply be its PR campaign. We wouldn't even be able to tell if it was successfully achieving its "goals" or not, assuming an AGI even has "goals"