The common abbreviation for percentage points is: PP. I'm not quite sure whether "%P" is comprehensible - I would rather use the commonly used abbreviation or write it out - to be on the safe side.

Hope this helps.
Regards,

You don't use this p in English. You just write "13%". Everyone with basic maths knows what the symbol % means.

Well, there is a difference between 13 percent, and 13 percentage points. Which, I suppose, is the point the OP is trying to make. I am not aware of a universally understood abbreviation, however.

They mean exactly the same thing.

No they don't John. A rise from 26% to 39% is a rise of 13 percentage points on the one hand, a rise of 50% on the other.

@John:
http://en.wikipedia.org/wiki/Percentage_point

Thanks, everyone. I've decided to use vanilla's "PP".

Es gibt schon einen Unterschied zwischen "Prozent" und "Prozentpunkt" - das eine ist eine relative Angabe, das andere eine absolute.

Wenn sich etwas von 1 % auf 2 % erhöht, dann ist das einerseits eine Verdoppelung (plus 100 Prozent), aber auch eine Erhöhung um einen Prozentpunkt.

In diesem Fall hast Du wirklich unrecht, John.

Oh, OK, I see what you'll are driving at.

wikipedia

Percentage points (pp) are the unit for the arithmetic difference of two percentages