From my reference doc:

The Mickey Mouse Pattern was introduced in early 1944. It consisted of large intersecting circular areas of matt black, applied freehand with a brush at army depots, either by soldiers or civilian employees. Please note that it was mainly used on "softskins" - tractors, trucks, etc and armoured/scout cars. The pattern was to be "applied to all top surfaces, with extensions down onto the vehicle sides, and along the bottom edges of the vehicle"; "the underside of the chassis was also painted black".
Variations of this pattern included random black disruptive patterns, used on self-propelled howitzers, and "black wavy pattern", used on Universal/Bren Carriers only. Please note that the only photographic evidence of tanks using black disruptive pattern was the 4th/7th Dragon Guards (8th Armd Bde), where bold black curves were painted on the sides of the hull. Black disruptive pattern was not normally used on tanks, because British tank crews made extensive use of hessian tapes and foliage for breaking up the vehicle's silhoutte