If they try to hire for more positions than in the past they're probably growing, conversely they might be stagnating if it's the other way round.

If they hire people with specific skills it might also tell you what they're up to right now like going public or working on a new, supposedly secret project. Take Apple for instance. A notoriously secretive company, previous new projects like the iPhone, the Apple Watch and most notably a self-driving car have first been revealed by their own job postings.