A cutline is more or less the same as a seam. On some marbles people are more likely to say cutline (marbles such as MFCs). And sometimes I say one or the other without thinking why.
I don't what to make of that cutline. Is it the only one visible?
Nothing about it particularly said Vacor to me ... but since I didn't recognize it as anything else, I went to my favorite Vacor page.
So, this is my guess. https://www.billes-en-tete.com/detail.php?id=119
Stephen, I think your crease is a cold roll.
What kind of marbles did that one come with? This Vacor is my only specific guess. If it's not this, I'll sit back and wait for someone else's ideas. https://www.billes-en-tete.com/detail.php?id=211
Is that sunlight filtering through? It's artistic but it's throwing me.
Can we have a view in different light of that seam that's peeking out on the bottom left view?