How should time as safety pilot be logged?
The rules for safety pilots are spelled out in 91.109c but don't specifically state how the safety pilot should log the hours. 

However, the common consensus I've heard from friends is that you can indeed log safety pilot time as PIC time. The August 2015 Flight Training magazine had an article about this actually. Here is what they said:


  What is implied but not specifically stated in the regulation is important. Because safety pilots are responsible for determining the safety of the flight, they can log their right-seat time when the left seat pilot is wearing a view-limiting device as PIC time. This transforms time spent serving as a safety pilot into a truly valuable educational experience that will also expand the flight time totals in your logbook


Edit: I did some more research into this. 

PIC time is defined in Part 61.51(e). Safety pilots can qualify as PIC under bullet iii:


  (iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted


There are some other things to be aware of when logging PIC time as a safety pilot (in addition to the requirements of 91.109c):


The two pilots must agree that the safety pilot is the acting
PIC. 
PIC time may be logged only while the other pilot is
"under-the-hood."
If something goes wrong you are the one that will be held responsible. I wouldnt take the responsibility lightly. 
The pilot logging instrument time must record the safety pilots name in their logbook under 61.51(g)(3)