In theory you could use them if an elite got you a domestic upgrade as a companion. A non-elite used to be able to get a sticker upgrade on a full Y fare, but that appears to be no longer the case. However, as a practical matter they are useless until you get elite status again. You cannot transfer stickers to another member. I had four that I earned as a Gold in 1999 that sat in my account until 2010 when I got elite status again. Of course, if current trends continue they will be very difficult to use even if you do find yourself a Gold or Platinum again. Upgrades for those folks are increasingly elusive, and if you are a higher level elite you won't need the stickers.