In 1972 and 1973, the two Pioneer spacecraft were sent out to explore the outer solar system. Being the first human-built objects to be able to achieve escape velocity from our solar system, it was decided to include a message should any aliens intercept them.

Carl Sagan was approached to design a plaque with a message from humanity, and Linda Sagan created the artwork, and the plaques were fixed to both spaceships.

Here's the plaque affixed to the craft, and let's take a closer look at the contents.

There's a schematic of hyperfine transition of hydrogen, a pulsar map to find our sun, a representation of the craft and our solar system... and some naked people saying hi.

Yep, we sent nudes and a map to our house into space. And this was controversial for quite a few reasons, even though it was probably proper Starfleet protocol under Captain Kirk.