Question about stealing belts has been asked multiple times, here's one answer

PaulD

Glenumbra. Have always found it on the ships near in a basket. Have not found it anywhere else. In fact, it's most often a particular basket. It's on the ships at Daggerfall, ship on the right, as you move down the docks, basket is on the right side near the entry to "The Hotspur". Above decks, not below.

If you don't get it on the first look, check all the other baskets, then log and try again. It's taken me a few tries sometimes, but it will show.