Mr/Mrs or Mr./Mrs.

British (American)
Mr (Mr.) – Mister (not usually written in full)
Ms (Ms.)
Mrs (Mrs.)

Notice the American version uses a dot in all these abbreviations.

Notice the dot for American and none for British.
Brit: Mr John Smith, Ms Clarke, Mrs Roe
Am:  Mr. John Smith, Ms. Clarke, Mrs. Roe

Not for Miss - Miss Green, Miss Smith, Miss 

British: Please send all your remarks to Mr Smith as soon as possible.
American: Please send all your remarks to Mr. Smith as soon as possible.