The International Flag of Planet Earth

While this design loses some points for being essentially a cheap extension to the olympic rings device, it definitely wins points for other semantic associations, namely that if you remove 3 rings from the flag, you get the international biohazard symbol, which seems a fair warning for any aliens we may encounter.

good pick. it's not quite the flower of life as suggested by the article. this one is a bit simpler, often referred to as the 'egg of life'.

it resembles a bit the first stages of embryonic development which is common between all humans. i think it would be a nice fit due to that as to me it's a good representation of how we all have a common start in life despite human diversity once it develops further. It's a stage from before we have our differences which separate us.

green or blue as backdrop is a good natural colour also non-specific to certain cultures. white would also be good, perhaps better as it represents light / all colours, with then the symbol being green or blue perhaps.