Research the glass's origin. Murano glass is made only in Italy; if you see a piece of glassware stamped "Made in China" or "Made in England," you'll know immediately it isn't true Murano glass.
Know how authentic Murano glass is made. Because of its one-of-a-kind "bubble" style, each piece of Murano glassware is slightly different. If you find two identical pieces of glass, they are almost assuredly not real Murano.
Look for the trademark of the Venetian Glass Consortium. Developed in 1981, this stamp features the words "vetri murano" (all in lower case) or the letters "vm" (again, in all lower case). This mark is only used by companies located on the island of Murano.
Visit the website "Murano Clowns" to learn about individual companies and their trademarks. The Consorzio Promovetro was founded in 1985 and represents 65 of the 100 glassworks on Murano; many of these companies utilize their own trademark or stamp to verify their glass's authenticity. "Murano Clowns" includes photos of many of these company trademarks and logos on its website.
Inspect the glass for the "Vetro Artistico" trademark. This trademark -- which became law in Italy in 1994 -- is a sticker that is placed on any piece of authentic Murano glass. The sticker is a white square with the outline of a purple wheel on it; a grayish-silver design resembling tongs is placed through the wheel with the words "Vetro Artistico Murano" at the sticker's bottom.
Ask for a certificate of authenticity to prove the glass's origin. Compare the name of the company on the certificate to a list of authentic Murano glassworks. Shop at stores that carry the "Vetri Artistico" seal.