am looking at a picture which shows two ‘Speedbirds’ on the side of what was then known as Headquaters Building, which later became Tech Block A (or the Kremlin!).. dont know if these were illuminated..they also look bigger than the one you’ve got… picture is in the ‘BOAC Book Of Flight’, published 1959…
yep try the museum guys…
http://www.bamuseum.com/contact.html

Neil