This company is apparently defunct.
According to E. C. Talbot-Booth, Merchant Ships 1949-1950 (New York: McGraw Hill and London: Sampson Low, 1949), Costeira was founded in 1891. Talbot-Booth shows the flag with a normal cross paty rather than the straight-edged one above. Flaggenbuch 1905 (1909 supplement) shows the cross as four isosceles triangles that don't quite meet in the middle.
The Companhia Nacional de Navegação Costeira operated coastal voyages between Rio and northern Brazilian ports (e.g., Natal, Fortaleza, Recife, Salvador). The ships were apparently quite luxurious, at least in first class, described in one account I found as um grande playground, with voyages considered a vacation in themselves. The line was nicknamed "Itas do Norte" from the names of the ships, all of which began with the prefix "Ita-." Supposedly the original owner was a man named Laje, which is a Portuguese word for "stone" [actually "flagstone"] and ita means "stone" in Tupi. Readers of Jorge Amado's novel Gabriela, cravo e canela (Gabriela, Clove and Cinnamon) may recall that it was an Ita ship that carried the protagonist, Mundinho Falcão, back and forth from Rio to Ilhéus, the grounding of which provoked the dredging of the port that was an important part of the background of the story. Costeira was nationalized at some point before 1942, then merged in 1966 with the government-owned Lloyd Brasileiro to form "Companhia de Navegação Lloyd Brasileiro e da Empresa de Reparos Nacional 'Costeira', S.A." In other words, Costeira apparently became the ship repair arm of Lloydbras. Lloydbras itself was abolished in 1998.
And do Norte (meaning "northern") in the nickname Itas do Norte because the harbors served were northern Brazilian cities. Adding to the trivia, a well-known Brazilian traditional tune goes:
Peguei um Ita do Norte
e vim p'ró Rio morar:
Adeus, meu pai, minha mãe,
adeus, Belém do Pará!
(Morar and Pará do rhyme in most Portuguese-Brazilian dialects.)
This means "I boarded an Ita do Norte and came to settle in Rio: Farewell, my father, my mother; farewell, Belém of Pará." The latter is Belém city, capital of Pará, a Brazilian state. Belém, a common toponym in Portuguese speaking areas, is Portuguese for Bethlehem. Former Brazilian president Itamar Franco was named after one of these ships, for having being born aboard one of them--or so the legend goes.
Henrique Lage (not Laje, but still a pun because of the same sound) was one serious industrial magnate--shipbuilding, salt refining, first aircraft factory in Brazil, port and river navigation development, mining, benefactor of the military academy, close friend of President Getúlio Vargas (dictator of Brazil beginning in 1930), you name it. And founder of the Costeira Line. His estate is now the Rio de Janeiro Botanical Gardens, otherwise known as Parque Lage.