The following U.S. state names share an interesting property. Can you determine what it is?

California
Idaho
Maryland
Missouri
Nebraska
Oklahoma
Pennsylvania
Virginia

HINT:
It has to do with their postal abbreviations.

Answer:

Each state's postal abbreviation is also an abbreviation for something else:

California - CA - ca (circa)
Idaho - ID - identification
Maryland - MD - M.D. (Medical Doctor)
Missouri - MO - modus operandi
Nebraska - NE - northeast
Oklahoma - OK - okay
Pennsylvania - PA - public address - Physician Assistant
Virginia - VA - Veterans Administration