Real Handmade Ryukyu Glass Made in Okinawa

A lot of Ryukyu Glass is made in Vietnam. What are some real indicators to look for if I want real Ryukyu Glass made by hand in Okinawa, short of stickers or labels? Glass thickness? Specific feel of pontil mark?

Specifically looking to buy at second hand shops where stickers or labels may not be on them.

by Ryudai89