Agreed w/ tP. At most, I've heard of other systems encrypting partial numbers in the site and e-mailing like the missing middle 4 digits or something to the store owner. Then you're safe if the site gets hacked and safe if someone gets the e-mail... but screwed if someone gets them both.

This isn't a core feature of Ubercart, nor would I suspect it's easy to implement. Not impossible, but not super simple either.