In the U.S. I believe it's customary to refer to strangers as Sir or Ma'am
-Crow Sister

This isn't true across the board. It depends on one's upbringing and-maybe also which region of the nation a person is from. Among African Americans,some children are raised to refer to adults as sir or ma'am and others aren't (I wasn't. If some adult asked me a question, if I didn't hear the question, instead of saying "Ma'am?", I said "Yes?". It was considered very rude and disrespectful for either "group of children" to answer "What?".)

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However, my central point was that historically-in 19th USA and earlier-BlackAmericans were not given the respect that White Americans routinely received. Few White people (from children on up) used the titles Mr., Mrs., or Miss along with a last name for Black people. (And yes, some Black people had surnames prior to emancipation.) Instead, the titles Auntie and Uncle were used along with a first name.

Also, few Black women were referred to as ladies. Instead, they were referred to as "mammy".

I wondered if reviewing historical records of contacts between Black people who resided in England prior to the immigration of Black Caribbean people (which I'm certain exist-the records that is)-if those same customs were practiced in England.