Parker Horwell and Kirk Ltd were engravers, and the Southwark Borough Commercial & Industrial Guide gives their address as 14 Southwark Bridge Rd, SE1, where it bridges over Park St. There are now 2 large blocks on each side of Park St, Rose Court at 2 and City Gate House at 22, and nothing between. I think this building was on Park St with an entrance on Southwark Bridge Road, with the large OXO advert facing the main road.
There is of course a far better known OXO advert around a kilometre to the east on the OXO Tower, built into the architecture of the Liebig's Extract of Meat Company's factory to get around a ban on advertising on the South Bank. Presumably there was no such ban away from the river.