periods with initials and abbreviations
Periods in initials and in shortened titles.
In initials, put a period after each letter: U.S., a.m., p.m. In a shortened title, put one period at the end: Dr., Mr., Mrs. Write US without periods only in tables and tight labels. Do not write US. with a single period.
Examples
Use U.S. mail
Use Dr. Lee
Use 9 a.m.
Avoid US. mail