Luka Doncic can appear to lack no superpower on the basketball court, where the 22-year-old Slovenian star regularly treats N.B.A. fans to long-distance floaters, nutmeg passes and playoff fireworks. But cyber sleuths have been flummoxed by the inconsistency he displays during a more pedestrian task: writing his name.
Many collectors believe that an elegant signature of Doncic’s name on the lone copy of a basketball card that sold for $4.6 million this year was written not by him, but by his mother. Like the signature seen on many of his other highly coveted trading cards, the blue script is not the tilting scribble Doncic used during his teenage years.