Adding SMA conectors to a device whose metal casing is connected to earth ground through at a single point
Do we have to connect the body of the SMA connectors directly to
  signal ground, connect the chassis of the device directly to signal
  ground and not have the ESD guard ring? (image B)


There is a choice here, and it depends on what you want most. If the signal of the SMA connector needs to be impedance controlled (like high frequency RF) then don't separate the planes. A way to tell if would be to ask yourself this question: Would cutting the shield (somewhere on the cable that goes to the SMA connector) and inserting an 0.1Ω resistor affect your signal (0.1Ω would probably be similar or worst case to the impedance between chassis and signal ground). If it would then don't tie the shield to the chassis, go to the PCB signal ground.

If the signal isn't affected by impedance, and ESD is the major concern then tie the SMA shield to the chassis ground. 

Something noteworty: 

PCB's can have two grounds, there are many boards that I've built that have a chassis ground solely for ESD events which I've attached shield's to. In some cases I've even used a fastener for the PCB chassis ground. If an ESD event hit's the shield, the current from ESD goes out down through the fastener and returns through the chassis. (away from sensitive electronics). If there are two grounds, make sure there is clearance between the two grounds on the PCB