These are Dual Single Speed cogs or Dingle Speed, that work like normal single speed cogs. The difference is that you can stop the bike, loosen the back axle, and change over to the opposite cog. This comes in handy if you underestimate your climb or underestimate your energy level or whatever. It allows you to fine adjust your cadence to match the riding conditions.
The cogs are also made to be the same width as my normal single speed cog, so they can replace each other at any time without having to adjust spacers.
They have the same look as our single speed cogs. Just Dingle.