If you are signing a letter on behalf of the head of a company -- and using their letterhead -- do you sign their name followed by your initials in smaller writing? Or do you sign your own name and then put "on behalf of ____" [the letter writer]?

Thanks for your help.
From Wikipedia:

A common usage of per procurationem occurs in business letters, which are often signed on behalf of another person. For example, given a secretary authorized to sign a letter on behalf of the president of a company, the signature takes the form:

p.p. Secretary's SignaturePresident's Name
President's Namep.p. Secretary's Signature

Commonly in practice, an alternative form is used:
Secretary's Signaturep.p. President's Name

Somewhere at English Forums is a lengthy thread on this topic, but I cannot find it.
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Write the initials p.p. before your signature, which should be above the person's name for whom you are signing. The initials p.p. is Latin for per procurationem (per pro) and means the power is delegated to you to sign on that person's behalf and is used commonly in the business world. It is sometimes seen vice versa: p.p. before the other person's name, but this is a common mistake.

Read more: How to Sign a Letter on Someone Else's Behalf | eHow.com http://www.ehow.com/how_4798552_sign-letter-someone-else_s-behalf.html#ixzz0yoSpFdoO
For the secretary signature it's the secretary's name or the presidents name just signed by the secretary? Thanks

when signing on someone behalf do a they need written authority before signing

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