Fans, who are currently playing Valve's "Team Fortress 2," have probably spotted a couple of references pointing out a possible alien invasion in some maps — either in the form of a poster or a sighting of a UFO from a distance.

According to the report by GameSpot, oddly enough, there have been a couple of fans who have already spotted this kind of early warning in-game. Some of them have seen posters posted around the map which read, "BE AWARE UFOS IN THIS AREA." However, the most surprising one of them all is the reference to the hit '90s Sci-Fi TV Show, "The X-Files," in which the poster reads, "I WANT TO BELIEVE."

There are also other documented sightings of an actual UFO, which can be seen hovering over the distance. View the recorded clip below taken by YouTube user waterandroid.

So far, there have only been three possible theories to explain this kind of phenomenon in "Team Fortress 2." As speculated on GameSpot, the first would be an upcoming Halloween event from Valve that is pretty much identical to what the company did a few years back on October 2010, where they featured the "Horseless Headless Horseman." This year, the theme could possibly revolve around UFOs and Aliens. The second theory, is that a developer or the whole team behind the team is/are simply excited for the return of "The X-Files."

And the third is the rumored "Invasion Update," which has been circulating on the Internet since last July, as can be seen on this fan's post on "Team Fortress 2's" Reddit.

Unfortunately, for the time being, fans can only speculate on these UFO sightings, as Valve is still keeping the lid tight on this matter. Plus, it might also be a surprise for gamers.

For the fans who are skeptical about these sightings, they can check out some maps in "Team Fortress 2" and for those who still don't have it, the game is still available on Steam for free.