abs() of this value also happens to exceed the maximum positive value. Which means that in C, a simple negation can cause signed integer overflow -(-32768), and therefore UB.
Yeah, I think it is funny that in a standard binary, it would replace negative zero and makes some sense. In two's complement, it replaces the minimum value.
Fair that sentinel value is sentinel value, I suppose. But it is not like it is not a known and unique number in that encoding.