Technically, the current way is a fine way to start a sentence. "Fallen trees provide signs of strong winds." "Groaning sounds provide signs of zombies." The problem is that such a beginning doesn't fit with the rest of the sentence. For instance, it could say "Deserted guard posts and fires provide signs of life, encouraging you to explore deeper into the island." Or, with your suggestion, a second change would be needed to make it "The deserted guard posts and fires provide signs of life and encourage you to explore deeper into the island." And then the last sentence says "you" at one point and "they" at another, which is also a problem.