it's a 'null' sign standing in for his lost boy - lost to cancer
(,
Mon 3 Nov 2003, 16:08,
archived)
the overall effect also looks like a bike, if it were drawn by whoever did the opening credits to Poirot (the ITV late '80s/early '90s version starring david suchet)
(,
Mon 3 Nov 2003, 16:14,
archived)