Possible Clues:

• Clue in the mud
• Area of coverage for tinpot criminal
• Mark made by one progressing in Oxford, perhaps?
• Shoe impression
• Profit not fantastic in sign from Friday?
• Pay for picture, creating an impression
• Profit not unusual in area taken up
• Impression of Oxford? Type given by foundation
• Evidence washed away by the tide
• Profit not unusual in area where broadcast is available