This Walking Liberty Half Dollar has to be the most incredible mint error in the series. Not only is it struck on a silver Quarter planchet, it is also double struck. The second strike is 50% off-center with a uniface obverse.
Even though there is no date, it was struck at the San Francisco Mint since the "S" is clearly visible. It is in gem mint state condition and was recently certified by PCGS. It is also the cover coin of Issue 24 of Mint Error News Magazine.