Beware of this auction: "Authentic Jackie Robinson Game-Used Bat. Extremely Rare". Here's the link:
http://cgi.ebay.com/Authentic-Jackie...QQcmdZViewItem

Notice the registered trademark symbol after the word Slugger in the centerbrand. This was first introduced in 1965, well after Jackie's playing days were over. Furthermore, note the registered trademark symbol above the d in the word Powerized. This was first introduced in 1973. Perhaps there are other issues with the bat as well, but it seems painfully obvious to me that this bat could not have been used by Jackie Robinson during the 1951 season, as the seller suggests.

Kevin