Ryanair identify Reserved seats by placing an A4 piece of paper printed with "Reserved Seat" on the seat!
If you don't need the extra legroom I recommend you reserve seat Row 2A, B or C, this is because Row 3 behind is often blocked off (so you won't get tall people's knees in the small of your back or kids banging the tray table behind you). Also you can keep your loose belongings with you and not have to put them in the overhead locker for take-off & landing (which you must do if seated in Row 1A, B, C or Row 2D, E ,F (there's no Row 1D, E, F).