Specifically for 2nd Northamptonshire Yeomanry (& then 15/19th KRH), as shown here:

IWM original caption: Cromwell tanks of 2nd Northamptonshire Yeomanry, 11th Armoured Division, passing through Flers, 17 August 1944. (The date suggests that it may just be 15/19KRH though).
So what's happened here?

IWM original caption: Cromwell tanks of 2nd Northamptonshire Yeomanry, 11th Armoured Division, passing through Herouvillette, 14 June 1944.
That looks like '49' (or at a pinch 48). The only AOS of that era that I can find that corresponds to 49 are some RE formations or the RM Commando Engineers! It's clearly a two colour (green/blue background), and the RE units were blue. So mistake or remnant of an older scheme?
and just for completeness, a Challenger from 2NY from the same photographic series as the first photograph.
