Shibboleth

A port case put out with the rubbish in our street today.

Also... not something you'd want to be admitted to hospital with :-) Sorry! Remember the TV adverts?

A shibboleth is:

any distinguishing practice which is indicative of one's social or regional origin. It usually refers to features of language, and particularly to a word whose pronunciation identifies its speaker as being a member or not a member of a particular group.
[Wikipedia]

The word originates from a story in the Hebrew Bible in which pronunciation of the word "shibbólet" was used to distinguish Ephraimites, whose dialect lacked a sh sound (as in shoe), from Gileadites whose dialect did include such a sound.

Around Bath, two place names act as mild shibboleths - Frome, which pronounced froom but which outsiders tend to call froam, and Keynsham (where Kraft is about to close the Cadbury factory) which starts with a kay sound rather than with key. I'm sure there are lots of others.