For Lolly, it's her flower. Just the contradiction of a dead death having a flower over her ears just 

For Emerald, it's her bird autism. It always is nice to have an excuse to draw birds, or come up with bird accessories to have around her house

For Isham, it's her broken nose. It takes away one of the weaknesses of being a vampire (garlic repels them because of the stink and they have really good sense of smell) just by giving her a bigger "weakness"

For Kno, it's either her feathers, because you don't really see many women with "body hair", or her mutinous because it really does become a very interesting challenge to get across what she's trying to "say" with just facial features and body language. Also making her illiterate so I can't use her writing things down as a crutch

Esen-Ali, her cleft left arm. It just looks cool and certainly does give her a distinct silhouette, even discarding her sash and hair
