Pro (or per) procurationem ("by proxy"). It is sometimes also abbreviated ppa.
pp...it's an abbreviation for the Latin "per procurationem".it is used by any proxy when signing a document on behalf of somebody else.though..many say it comes from "proxima persona" :) (false, i...
fraud or impersonation I think
the person whose signature is on the letter
The usual is p.p. - which stands for pro percurationem inLatin