Am guessing, but is this the example of HQ tank with a number 7?
The above is a
Divisional HQ vehicle as indicated by the AoS marking - white 40 over black.
Numbers were not always used inside the tactical markings. Many photos from early in Normandy show a large tactical number located on the turret rear separate from the geometric shaped marking. A painting from this period shows another example, with the tactical number found on the lower remnants of wading gear.
regards,
Jack