From experience you can normally pop in and out without seeing anyone (EU so might be different on other servers). I think you still have to opt in even inside the areas as well.
The only quests I've seen for these areas have been to go to the safe zone towns on the edge, so if its one of those then you're definitely safe.
Depending on how crowded it is you should generally be fine.
So, how PvP zones work: If you are not flagged up, you cannot attack others who aren't flagged up. If you are flagged up, you can attack anyone, but you can also be attacked by anyone, whether or not they are flagged.
I think you have to mark yourself for PVP to actually be able to attack or be attacked. At least that is what I understood when the tutorial messages popped up while uncovering the map there. Never got attacked while riding through there.
That’s what I thought too, except I definitely didn’t mark myself and a lvl 60 attacked and obliterated me the second I stepped out of the town next to the PVP area
When you go Bloodmarked, you signal yourself to the other players in the instances, a substantial proportion of which are there solely to zap / flatten /hemmorhage you into a mushy pulp.
If you enter the region, you open yourself up to the same risk, but without the added risk of advertising your own violent intent. And without the potential bonuses that flagging brings.