All values greater than or equal to &H8000 (16-bit) or &H80000000& are negative numbers

They are stored in the form NOT(X)+1. Example: -1 = 1 + NOT 1 = &HFFFFFFFF.
In fact for all integers X, -X = NOT(X) + 1.

&H8000 = -32768
&H80000000& = -2147483648

On a PDP-11, ones complement is used instead of two's complement.