The trouble is that the preambles aren't true. If you hear "Your
attention please; here is a special announcement ..." you can
guarantee that there will be absolutely nothing special about the
announcement.

On the Jubilee Line, every so often the in-car displays flash
"IMPORTANT" several times (or a similar word, I forget exactly). This
is followed by a message telling you to take your bags with you when
you get off the train.

On the Toronto subway (underground) these days, the TTC has a regular
program of stupid pre-recorded announcements in the stations. Show your
student ID card when paying student fares! Don't try to board a train
after the door-closing chime! On weekends a Day Pass can be shared!
No smoking on the TTC! Take all your belongings with you when you leave
the train! (The actual wording in each case is significantly longer.)

They always play them in pairs -- and, lately, each pair of stupid
announcements is preceded by the same attention-getting melody.

On other other hand, when they actually have something to announce that
you need to hear, i.e. about a service problem, (1) they just announce it
without the melody, and (2) half the time you can't make out what they're
saying.
--
Mark Brader | "What a strange field. Studying beings instead of mathematics.
Toronto | Could lead to recursive problems in logic."
| -- Robert L. Forward (The Flight of the Dragonfly)

My text in this article is in the public domain.