Whats the silver thing on Isshin's arm and if he was a captain why when he goes shingami doesnnt he have a white jaqueta like the rest

If you look at Isshin, you will notice that he has a long white like scarf on his arm.. That's his white jaqueta as a captain. I think he dont want to wear it so he used it as a scarf like..

he does not hav a jackt because its that cloth on his sholder.