Arecibo Message to Aliens - 1974
The image on the left, actually in binary code, is the translation of a radio message that was beamed into space in 1974 on the occasion of the completed remodeling of the Arecibo Radio Telescope [see complete article].
It includes basic DNA information including the average human shape and height along with world population -- a simple greeting that will not be returned for 50,000 years due to the 25,000 light year distance between earth and the intended target, a globular star cluster within the Constellation Hercules. Of course, by then there won't be anyone left on this planet.
Hopefully, like the New World in which the original Thanksgiving was celebrated, we will have moved to a cooler planet, like the one of the original garden in which Adam and Eve were placed before their descendants messed it up. Such are the perils derived from snacking at the Tree of Knowledge of Good and Evil
Now, if there's a lesson in this for aliens -- assuming that before they figure out and answer our binary DaVinci Code-like missive they will have stumbled upon a history of the first Thanksgiving event and realized that Native Americans were soon to be treated to an after dinner morality play, fashioned just for them by the Pilgrims of European Puritanism -- it is that messages from Earth sometimes are really just phishing spam.