In Moed Qatan 27a, the gemara refers to a certain type of couch or stool as an ערסא דגדא: a couch of fortune. Rashi explains it as a couch that is only used for showcasing mazal tovs:

מטה שמייחדים אותה למזל טוב ואין משתמשין בה כלום אלא מייחדין אותה לשרות מזל טוב עליה

"A couch that is designated for a mazal tov. It is not used at all, save that it is designated for the placement of a mazal tov upon it."

What is this mazal tov to which Rashi is referring? A good luck charm?