A colleague of mine has been suggesting that he might open all of his lectures with a slide showing this picture:
This seems like a good idea. After all, it cannot be doubted that a mobile phone ringing in the middle of a lecture or a seminary is a distraction. It is worth having a subtle reminder to students about acceptable behaviour during a class. This did make me wonder though - there is a whole language of signs which could be used here, and perhaps subliminally flashed up on the screen during the lecture in the kind of way which works so well for Darren Brown.
For example, since it is equally distracting to have students on Facebook or tweeting your latest terrible joke during class, you could have:
And since there is always a good chance that I am having a bad hair day, I would personally like to have:
Of course nobody likes it when a student arrives to a post-lunchtime lecture with one of those awful polestyrene trays full of chips, so it would be remiss not to have: