The map in the police department showing Middleton and surrounding areas is actually northwest suburbs of Chicago.
The "whistle" that Cassie gave Martha is a Bos'n's Pipe. It is used aboard Navy ships by the Bos'n's Mates to call the crews attention to various announcements. They use different calls depending the the type of announcement.
For the first time a character uses the term "The Good Witch", when Martha Tinsdale uses it.