The title of a business memo is the word MEMO or MEMORANDUM, in an appropriate font style centered at the top of the first page. Printed in bold uppercase letters it informs the reader that the document is an internal communication.
There are no hard and fast rules governing the size of the letters but the font you select should be sized one or two points larger than that of the text found in the actual message. Standard message text is 12, so select 14 or 16 on your toolbar. Try each one on for size and pick one that pleases you.
Stick with your choice in all future business memo writing as a consistent visual appearance will help your readers develop the habit of recognizing the communications that come from your desk.
On a preprinted memo sheet the title word MEMO will appear below the company logo and above the heading.