Which is the right way to use these pedals?

[DebW]

wouldn't they be marked R and L?

They are usually marked L and R, but in any case can only be installed one way since the left pedal has left threads and the right pedal has right threads.

We call the ones pictured in this thread "bear traps" because of how they chew up your shins.

Rat trap pedals is another name. Bear trap must refer to the leg-hold type animal traps? Rat traps look like mouse traps, so that analogy is not as obvious.

This is also called a platfrom pedal, AKA flats:

Yes, any pedal that supports much of your foot and can be used comfortably with a soft-soled shoe. The ones you picture are also called BMX pedals, as they have small studs to keep your feet stable doing BMX jumps.