The ankh is a very ancient Egyptian symbol which is today interpreted as meaning "eternal life." The shape of the ankh is a tau cross surmounted by a circle. This may represent the union of the male (cross or trinity of points) and the female (the circle or yoni). Because is it often held by the loop by Egyptian figures, it is known as the "handled cross" or crux ansata. It is also known at the Key of the Nile, the Key of Life, the Knot of Isis (the shape may originate from the knotting of a strap to fasten clothing), and the Sandal Strap (it looks like a sandal strap where the heel would be in the circle).
The symbol of the ankh may also represent the sun rising over the horizon. This can be seen in the Ghost Hunters logo where the circle is formed as a solar symbol, the circumpunct.
The ankh was famously used as a symbol of Sanctuary in Logan's Run. Here it may connect to the idea of the ankh representing a sandal strap as the people who wear the symbol in the movie are known as "Runners."
In Ghostbusters, the title sequence has the word Ghost above the word Busters so that the "T" in Busters supports the "O" in Ghost forming a slightly veiled ankh.
In the SyFy channel series Ghost Hunters, the logo combines the words "Ghost" and "Hunters" in much the same way as the above example, so that the letters "O" and "T" for a veiled ankh.