The boy told his grandfather he had just seen James Bond and asked if they could get his autograph.
Moore happily signed the boarding pass, the boy, however, thought there had been a mistake because the autograph didn’t say James Bond, but Roger Moore.
The grandfather apparently had no idea who the actor was, but being a dutiful grandfather, went over and asked.
Grandpa went back and explained the situation and Moore then explained to the boy that he had to sign his name as Roger Moore because otherwise “Blofeld might find out I was here.”