Plaque

There is an identical plaque on the other side of the street, immediately opposite.

Naming both these blocks as 'Rosebery Square' seems odd given there's a main road running between them. This 1901 insurance map shows that at that time 'Rosebery Square' referred to just the area partially enclosed by the U-shape of the tenement block on the west. It also shows that substantial storage space was created under the road at the time it was built, which was when Rosebery Avenue itself was created, 1887-92.

A London Inheritance has a good post on this area and the development of Rosebery Avenue.