Possible Clues:

• Bookies' way of communicating ploy when exchanging letters
• ___-toe (game with X's and O's)
• Nervous reaction, dangerous act used by bookmakers
• Signs that may be warnings to lay off
• Breath freshener
• How intelligence is imparted at Cheltenham, for example
• As a matter of course there are signs of this
• Russian water-urn
• Method for transposing signals
• Bookmakers' signals