A Cup With A Difference

This cup is one of my collection of vintage & antique glassware such as, Tumblers...Cups...Beer Glasses...
I do have some interesting pieces such as this cup...I have not seen a cup with the seam going around the middle & I can't seem to find any info on it as far as an era or maker...There are no distinguishing marks...

I hope someone can shed some light on this cup...I would be very grateful

Thanks for looking