I'm looking forward to Palworld models popping up on Models Resource or the like so I can do some comparisons on my own. That Azurobe model literally just looks like 3-4 mons thrown into a blender.
I always just thought of it as, the uppermost bit is that power of two but negative. So for four bits from right to left, if they're set to one you add 1, 2, 4... -8.