I think I answered at least one of my own questions doing some searching on the thread.
The mystery "pin" in the upper corner of the body of my little Chas. Parker made jewelers' vise, near the edge of the swivel jaw, appears to be the location of a pin (or perhaps a button?) on some models. I am guessing to release the swivel jaw?
The thumbnail is a Chas. Parker owned by
kenc184. It shows a pin or button located exactly where there is a round area of steel different than the body on mine, like a pin that was cut off and made flush, or a hole for one filled in. He posted more photos in this thread
here.
I am hoping
kenc184 sees this and chimes in with an explanation for what that pin/button is. Or
anyone with a Chas. Parker swivel jaw vise with that pin/button in place. Perhaps the swivel jaw on mine is not meant to be completely removed? Maybe that's why there is only the hint of where a pin/button normally goes.
And while they are confirming that conjecture, would they also please see if there is a dimple on the top of the swivel jaw directly over the swivel pin, too.
EDIT: Slaps self on forehead... Okay, after thinking about this a little longer, I am starting to think that IS the remains of a pin and a PO (perhaps the antique jeweler who owned the antique workbench!) sheered the pin off inside the body of the vise and finished it off flush. Now I am wondering if I should try to drive it out with a drive pin punch. It probably wouldn't need to have a protruding end to work as intended (inside the channel of the swivel pin/boss), it would just have to be re-inserted and left short inside the pin hole on the other side.