The print on the back, identifies it as a STO
(Stamped to Order)
Postmark Killer 86 (2)
BLACKBURN LANCASHIRE EKU 1st October 1906
Blackburn 1906 (clock tower with "Time Ball" ) Navigation.

"I read the news today, Oh! boy, 4000 holes in Blackburn Lancashire" (John Lennon, "A Day in the Life")
(4000 potholes in the roads)
Also exists on thin paper (Newspaper Wrapper)
