It would be best if you could include some of the subtitles that use this term.
But here is a good explanation from Literature SE:
Most likely from the Hebrew word "סיסמה", which translates to
The pronunciation of the word out loud is (approximately, going off
information a native speaker told me) "seez-ma" or "sees-ma".
Now this provokes the question:
In the story, Ali Baba's brother became trapped in the cave and
couldn't get out. He did try other grains though... If the phrase was
originally something like "password" or "password for opening"
(literally), why would he guess other grains?
However, it turns out that tale wasn't originally in The 1001 Nights.
It was first seen in a French translation by Antoine Galland.
Galland claimed that he heard the folk tale in Aleppo, Syria. However, some scholars argue that Galland made up the story himself,
since no documentation of the story in old Arabic records has ever
been found. It does not appear in the oldest copy of "The Thousand and
One Nights," which is an Arabic manuscript from the 14th century. In
"One Thousand and One Nights," the storyteller Scheherazade tells "Ali
Baba and the Forty Thieves" to her husband, the Persian king Shahryar.
TL;DR: Galland claimed it's a Syrian tale, but it's most likely he
made it up. It's not in the oldest version, plus the making-it-up
explains the other grains.
If he made it up, it's most likely that "סיסמה" (seesma) became
It needs to be noted, however, that the phonetic similarity to "sez-uh-me"/"says-me" has long been harnessed by writers (and jokesters) to add a little "spice" to dialogs. And the similarity to "see-same" is perhaps even more popular with jokesters.