People searching for extraterrestrial life have long been on the lookout for a message or signal of some sort. But what if we found life on other planets thanks to the chemical footprint they leave on their home worlds and colonies? E.T.'s hairspray could turn out to be more useful to us than any of his broadcasts.

Hairspray and many other industrial products used to contain molecules called chlorofluorocarbons, which are made up of the elements carbon, chlorine, hydrogen and fluorine. (CFCs were phased out starting in 1989, after many countries signed onto the Montreal Protocol in an effort to stop the depletion of the ozone layer, and have since been replaced by alternative chemicals.) Like carbon dioxide and ammonia, it is a greenhouse gas that absorbs and emits heat; unlike carbon dioxide and ammonia, CFCs do not occur naturally.

So, if scientists can pick up the signature of CFCs in the atmosphere of a small planet orbiting, say, Alpha Centauri, the odds would be good that some intelligent form of life is present.

"An industrialized civilization will be one that will use its planetary resources for fabrication, the soon-to-be-detectable-from-Earth atmospheric byproducts of which could be a tell-tale sign of their activity," astrobiologist Sanjoy Som of nonprofit organization Blue Marble Space Institute of Science told on Monday.

Blue Marble scientists are raising money to look for signs of alien hairspray in space, through the science research crowdfunding platform Petridish. They're seeking at least $24,000 to fund their next research paper, and donors can get a front-row seat for lab meetings as the work progresses.

Several members of the Blue Marble hairspray team also published a paper in the journal Astrobiology in 2011 aimed at a similar method of finding extraterrestrial life, by detecting biologically derived sulfur gases. Certain sulfur compounds are only made by degrading algae as far as we know, so detecting those chemical signatures around an exoplanet would mean that some kind of life existed there -- perhaps not an industrial society or even anything remotely sentient, but still some sort of extraterrestrial.

The group found that it is possible to detect these signatures from Earth, and it is even easier to pick up traces on planets orbiting M-class stars, a group that includes red giants like Beta Pegasi and red dwarf stars like Barnard's star.

“A characterization mission could detect these organic sulfur gases -- and, therefore, the life that produces them -- if it could sufficiently quantify the ethane and methane in the exoplanet's atmosphere,” the authors wrote.

On Earth, CFCs have been largely phased out due to their tendency to consume ozone, a molecule made of three oxygen atoms that occurs in the atmosphere. The ozone layer is vitally important for human life, as it absorbs harmful ultraviolet radiation.

Some scientists, however, have raised the possibility of bringing CFCs back to engineer a livable environment on other planets. In 1993, famed astronomer Carl Sagan coauthored a paper on terraforming methods. Sagan and coauthor James B. Pollack put forward several ways to produce Earth-like temperatures on nearby planets. One of the ways to make Mars more suitable for human life would be to fill the air with greenhouse gases like carbon dioxide or CFCs.

“Manufacture on Earth of enough CFCs to warm Mars can be readily foreseen, because in only a few decades with present technology we have managed to synthesize enough to contribute to global warming on our planet,” Sagan and Pollack wrote.

At the time, the pair estimated that it would be inordinately expensive, requiring rocket launches every day for at least a century. As an alternative, CFCs could be made on Mars from native materials.

But while CFCs would create a big blanket of gas that would warm up the Red Planet, there is a drawback. Just as they do in Earth's atmosphere, the CFCs would bind ozone and prevent any appreciable amount from building up in the air, meaning that Martian colonists would be bathed in harmful UV radiation.

“Perhaps this in turn could be fixed with a high-altitude layer of ultraviolet-absorbing particles, but the difficulty of planetary engineering on Mars is thereby greatly compounded,” Sagan and Pollack wrote.