Graffiti isn't just for troublemakers and wanna-be artists anymore. Astronauts on the International Space Station are now tagging in outer space, and it's just one of many odd interests astronauts have placed in outer space.

In the outer space equivalent of carving "I was here" into a park tree, Italian astronaut Luca Parmitano left his mark several weeks back with a visible sharpie message:

It's tough to see, but the black letters read: "Installed by your friendly Expedition 36 Crew." Inspired by this inscription, Universe Today looked into other hidden messages in outer space, and they did not come up empty, as NASA astronaut Tom Marshburn explained:

“We did a lot of maintenance during our flight and rotated out a lot of the experiment racks and we saw many signatures on the internal hull or on the inside parts of the racks,” Marshburn told Universe Today via phone from Johnson Space Center. “Things like ‘Greetings from the Water Recovery team!’ with everyone’s signature. That’s fairly prevalent on the inside, particularly behind the racks, but not in plain view.”

Like regular people, astronauts want to be remembered, even if it's only by other fellow astronauts. That desire for fame can take the form of Alan Shepard's lunar golf swing back in 1971, or, as Universe Today found, much more simple messages around the space station.

One particularly memorable object, according to Marshburn, was a toy Gort, the robot character from The Day the Earth Stood Still (left). In another discovery, a message above the funnel that functions as a bathroom reads "Blessed are those who wipe the funnel." A little inspiring potty humor never hurt anyone, even in the dangers of the great beyond.

Even the Mars Curiosity rover got in the act with a message of its own back in March. Intentionally or not, its tracks were shaped oddly like, well, something that would go into one of those toilet funnels.

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