Skull and Crossbones nebula, 18x7 min, TS115/0.75 reducer, L-enhance
I pushed the processing harder in this one in an effort to get the top of the skull to show up. It took me a while to figure out why it has it's common name, but the skull is obvious once seen - in this image the skull is tilted about 30 degrees to the right - got a bit of a Terminator look to it.
That's a pretty cool nebula. I too sometimes wonder how they get their names but I can see the skull as you described it and you're right it does look like the Terminator. I'll have to add this one to the 'To do list'. Love it!