Let’s say Lucy is in the bar with a dodgy bloke and wants to get away. Conversation goes
lucy - can you help me
barstaff - what with? You need directions to the station?
lucy - no, this bloke, he’s a bit …
barstaff - and what …
Lucy - I need to get away
barstaff - call a taxi sweetheart
Lucy - …
here, Lucy would have to be pretty forceful to get the help she needs, which for a shy person in a busy pub, may not work.
if the scheme works as it should, the conversation goes
lucy - is Angela here?
trained barstaff - Angela you say? Come over here and I’ll help you get a taxi. You can wait back here and go out the back so no one sees. You’ll be ok.
this time, the conversation quick and unambiguous.
so the key is training the barstaff. Whether or not dodgy bloke knows the codeword really doesn’t matter.