Most doors I come across in the Rage universe do not cause a hand icon to appear, indicating that they can be opened, nor are they locked with a grindable lock. Most actually display a white warning sign as seen here:
And zooming in a bit:
I have to admit I haven't been keeping track of doors that become open while you play, so I wanted to know what it is this icon indicates, exactly.
Does it mean "this door won't open at the moment", or perhaps "this is indeed a door, but it will never open"? Perhaps it means either one depending on the door?