For years the conventional wisdom of visitors to Mexico City has been to patronize only official taxis because many roving, unlicensed cabs have been operated by thieves looking for victims. Now it seems that some taxis that appear to be licensed are actually using phony papers and license plates. A recent report estimates that these “cloned cabs” represent 20 percent of the taxis on the street while cabs with no papers make up about 15 percent. Adding to the confusion for the safety-minded, many past assaults have occurred in legal cabs that had been stolen. The best approach still is to phone licensed taxis whenever possible. The good news is that taxi crimes in 2000 were down 14 percent from 1999.