In the 18th century, firefighters weren't always meant to fight fires. If your building didn't have a fire mark, they might just let it burn. The reason: fire insurance, and fire insurance companies. [CORRECTION: the plaques on the wall at 1:10 are parish boundary markers, not fire marks! The facts and words in the video are true, but those markers were misidentified in the sources I used. Apologies.]
Filmed safely: https://www.tomscott.com/safe/
SOURCES:
https://www.museumoflondon.org.uk/discover/how-great-fire-london-created-insurance
https://www.gresham.ac.uk/lecture/transcript/print/protecting-london-the-phoenix-rebuilding-london-after-the-great-fire-and-the/
https://researchonline.rca.ac.uk/4481/1/Miranda%20Clow_thesis_1%20of%202_Text.pdf
https://www.london-fire.gov.uk/museum/history-and-stories/