You're right about it being provided by insurance - my first inkling of this was seeing placards like the below, on old houses, in historic cities.
Here's a wikipedia article on fire insurance marks: https://en.wikipedia.org/wiki/Fire_insurance_mark
Fire insurance has over 200 years of history in America. The early fire marks of Benjamin Franklin's time can still be seen on some Philadelphia buildings as well as in other older American cities. Subscribers paid firefighting companies in advance for fire protection and in exchange would receive a fire mark to attach to their building.