Someone writing a thank you note to an employer should remain professional and courteous. It's best to use the employer's first name in the opening of the note and to sign the note at the end.
The body of a thank you note written to a supervisor should include specific information. It may involve thanking her for a recent promotion or raise, acknowledging her understanding for a recent crisis in the workplace or expressing general appreciation. While the note should stay as short as possible, it should include brief details about why the employer is being thanked. A thank you note should always be handwritten.