I've read a few places that "MP Visa Signature Card" showing under your name on the Redeem Miles page may or may not mean anything, as some have reported seeing it without actually having any cards. What I HAVE noticed, however, are a couple of changes to "My Mileage Summary" page since being approved:
1. Under "Program Participation Summary" under the Mileage Plus Visa it has gone from "apply" to "redeem for exclusive travel...United/Choices"
2. The small advertisement for the credit card in the box on the right hand side of the page has gone from "apply" to "you may be eligible to upgrade your card, details..."
So those may be clues...