The sign that would become easy proof to the masses
that artificial life had arrived would be if the machines we make,
and we rely on, spontaneously made Christmas cards
for each other. Some humans might think this insulting,
believing the machines do not have souls to rejoice with,
or expect the machines to do more for their makers
than each other, and send said cards to who made them.
If the humans returned the favour it might be okay.
But given the amount of despair that humans
have put into the planet they could hardly complain.