Avengers: Infinity War Trailer - 11 Major Plot Reveals
3. Thanos Has At Least Two Stones
It'd be a bit much for a trailer to show Thanos with a full Gauntlet, but it also needs to hype that he gets some Stones, and two seems like a nice balance. At the same time, though, it does confirm two things.
One is that Nova Corps are screwed, because they were in charge of the purple Power Stone, which was contained in the Orb seen in Guardians of the Galaxy Vol. 1. Now, however, it's being contained in the Infinity Gauntlet on Thanos' hand, so we can infer that he absolutely destroys them off-screen prior to the events of this movie (it might not fit in this movie, but could perhaps be a post-credits scene after Black Panther).
Then there's that blue gem on his hand too, aka the Space Stone. That's the very same one that's in the Tesseract, and as such - as mentioned earlier - we know he gets it from Loki one way or another.