Attention line
the attention line is internally used for the letter where the addresses are in the same company. it begins either at the left margin or in the center
The Attention Line is placed above the Recipient Line, that is, above the name of the firm to which the mailpiece is directed.
In formal correspondence, a line of text denoting the intended recipient within an organization. In a business letter, it is usually positioned above the salutation. In an address on an envelope, the United States Postal Service prefers that it be placed immediately above the organization name without "ATTN:".