Possible Clues:

• Evocative picture of bomb no Russian would pick up
• Small illustration at the beginning or end of a book
• Word-picture
• Half-a-dozen get another tennis fixture in the picture
• Small word-play
• Character sketch - give tent (anag)
• Brief incident
• Character sketch providing early start to vetting process
• Six and ten get interchanged, by way of illustration
• Sketch given out to test examinees, initially