The folks over at Uptown Almanac point our attention to a sidewalk square that was possibly -- but likely not -- signed by John Lennon. For some reason, the city seems to be going to great lengths to protect the square of sidewalk in question, at least if the picture above is any indication.
Unfortunately, this square at Fell and Stanyan almost certainly does not possess John Lennon's actual signature, because -- as various commenters have pointed out -- Lennon could not have been in San Francisco on either Dec. 5, 1969 or May 12, 1969, the two dates that could be indicated by the sidewalk.
Remember that in 1969, the Beatles' movements were being followed very closely. Existing records place John and Yoko in London on Dec. 5, 1969. Okay, but could the signature have been left on May 12, which is how a British person would write the date? It's possible, but, as the UE commenters have discovered, very unlikely. Records have Lennon on London on May 8, and also have him flying from London to Barbados on May 24, 1969. The reason he flew to Barbados? Because he was refused a U.S. visa. So it seems pretty doubtful that Lennon was scratching his name into an S.F. sidewalk on May 12, 1969.
Still, there is the strange fact that this little piece of concrete has persisted through who-knows-how-many resurfacings and remodelings, etc. And even if it's not real, it's still kinda funny.