riddle shield - spelling mistake?

[katrionabowman]

hi all from kt in seattle,

the following pic is a screenshot of tom riddle's special services to 
hogwarts award. but look at the spelling of "riddle!" they've spelled 
it "riddell." what will this mean for the tom marvolo riddle/i am 
lord voldemort anagram in CoS? does any one know why they've spelt it 
this particular way?

http://www.harrypotter.ws/movie/specialservices.jpg