2.4 (Guideline): Sufficient context should be provided with each question. Even when there is no other context, the subject area and type of document should be indicated. It can be helpful to enter sentences or paragraphs where the term in question occurs. See a more detailed description http://www.proz.com/faq/70204#70204. Here there are a host of possible scenarios.

Nevertheless, Nigel has given you a possibility and I could give you what I would term implausible, ridiculous and even stupid proposals, such as "Su Empresa/Entidad", or "Su Excelencia" (of course, I am being silly). Nevertheless, perhaps you could advise if the P.O. is an automatically generated one, as one possibility which comes to mind for "S/E" is "sin emisión". Do you know?

See some references below:
[PDF]
ÍNDICE I. OBJETIVO............................................................
www.adifse.com.ar/.../compras/Reglamento.pdf - Translate this page
File Format: PDF/Adobe Acrobat - Quick View
Sólo se podrán emitir Órdenes de Compra / Contratos a Proveedores /. Contratistas .... compra. (De $ 5.001.- a $ 15.000.-). ***Sin emisión** de orden de compra / ...


[DOC]
Logística Compras Descripción del sector La Gerencia de Compras se ...
adrtpa.googlecode.com/.../AdR%20MINO%2009... - Translate this page
File Format: Microsoft Word - View as HTML
Compras o gastos excepcionales, **sin emisión**
de Orden de Compra. ... Se realiza una Contratación Directa, a través de la emisión de una Orden de Compra por ...

Some companies may issue P.O. "sin emisión automática"

HTH!