Do I need a stamp for my USPA license?
I'm a USPA AFF, tandem, and static line instructor.  Your signed and completed A-License Proficiency Card is valid and USPA will process it without the stamp.  You only need the stamp if you want to go to another dropzone and use your card as a temporary license.

The proficiency card is only valid for 60 days after the date it was completed, so don't waste time sending it in.  The last I heard, USPA is taking 3-4 weeks to process license applications.

Edit to add:  Don't send in the actual card.  You can mail a photocopy, fax it in, or scan it and email it to membership@uspa.org.  Faxing or emailing will get you your official license a few days faster.