From 1925 to 1934, André Citroën rented the Eiffel Tower and had the Citroën brand name emblazoned with 250,000 incandescent lights. 600 kilometres of electric flex were required for the letters, which were 30 metres high.
Lowry probably saw the sign on his visit to Paris in 1926 with his school The Leys for a hockey tournament though he would have also seen it on his 1933-34 stay in the city; "the vertical sign which marks the seemingly ubiquitous Eiffel Tower: Citroën". ( The Cinema of Malcolm Lowry: a scholarly edition of Lowry's "Tender is the Night" Edited by Miguel Mota and Paul Tiessen Pg. 78).