If you really want to see the official documentation then it is here. Search for flicked which you will find at the bottom of page 3. There is a help line (bottom of page 4) which one can, presumably, ring so that they can identify the correct distinctive sound whilst you flick. You may also notice, if you can be bothered to peruse the rest of the document, that the id card is covered in the letters EU when illuminated with Ultra Violet light.