....
A good mate of mine drives an unmarked car (he's a very highly qualified 'specialist', not a speed cop). I know his vehicle well but keep getting messages from him (4 this year so far) that he spotted me at xx:00 hrs on the xx road travelling east/west/north/south, and this isn't just local - I get around!
When I asked him how come I never see him, he grinned and said "Robin, you're not supposed to!"