Looks kind of like a swirl to me. At that size and way the glass looks in the pics I'd wonder if it's a Champion new old fashion. With a twisted pattern.
I thought I had a match for the OP in my Vitro pile, but after rooting around these are all I could come up with (search continues)
Bottom right are obviously Pelt
Carry on!
Looks like one of those foreign marbles referred to as pincers (or pinchers, don't recall). Anyhow, machine made probably 50-70 years ago judging by the lots I've found them in previously