From PostalReporter.com reader: 

The website link  http://gx.gallup.com/pos [link corrected] started appearing at the bottom of customer sales receipt on Saturday. USPS requests customers to “Tell us about your recent postal experience.” All you need is a zip plus 4 of the post office visited (located at the top of the sales receipt) to start the questionnaire.

According to the website operated by the Gallup Organization: “Your questionnaire responses are important to help us improve postal service in your area. This questionnaire should be completed by the person who recently made a purchase at a local post office. Your responses will be kept strictly confidential.”  One of the questions asked is “How would you rate your visit to the __________Post Office?”

Below is a copy of a customer sales receipt