ma'am/madam

used in the same way "sir" is used for men, "ma'am" (or, infrequently, "madam") is inoffensive, but neither "sir" nor "ma'am" is extremely common today. Some people dislike it: "You're more likely to hear ma'am when somebody is annoyed" (Deborah Tannen); "In theory, ma'am is a courtesy term, meant to convey respect and graciousness lightly salted with deference. Yet much evidence suggests that when it comes to fomenting a sense of good will ma'am fails even more spectacularly than 'Have a nice day'" (Natalie Angier, The New York Times). Others like it, including Miss Manners (Judith Martin) and those familiar with languages where a polite title is tacked onto every interaction with a stranger. At one time, "madam" appeared to be losing its respectability because of its other meaning (female head of a house of prostitution). "Sir" never had an unsavory second job, but male-female word pairs (master/mistress, for example) often went in different directions. For someone connected with prostitution, use prostitute, owner/head of house of prostitution.