Hey, i wouldn't recommend a ribbon around their neck or their paws, rabbits have extremely weak limbs and if the ribbon got stuck on something you could potentially risk your bunnies' life. My suggestion for this is to draw with a marker on their ear, but also keep in mind that you need to use a non toxic ink and rabbits are known to lick and groom their ears, so you also might need to draw over it if the bun licks it off, you could write numbers (example odd numbers are males and even numbers are females) or you could distinguish them with different colours, example ( blue ink is males and pink ink is females) hope this helps!