Rising headcount is not necessarily a good sign. To the contrary, it's often a sign that the company is haemorrhaging cash, hoping that if they hire enough staff something magic will happen before time runs out.
There's also the idea that head count can signal revenue, or expected revenue. Companies looking to be bought can go on hiring sprees to appear more healthier to potential buyers. I experienced this at one company, when the new owner installed their CEO, the first thing he did was slash head count.