On englands roads what are those yellow signs with a black H on them with numbers?

Question

on englands roads what are those yellow signs with a black H on them with numbers. there are two numbers which are positioned above and below the horizontal line of the H. the signs are found on buildings, railings and at various points along roads, and im intrigued.

Answer 1

they are the house numbers of the local heroine dealer - thye are not found in liverpool or manchester as they could not fit all the numbers on the little yellow sign