Joe drove his car to a shopping mall and parked it there to attend a movie. The place where he parked was designated as a one-hour parking space on a sign at the entrance where Joe drove in. There were many similar signs around the shopping mall stating that people were parking their cars at their own risk. But this particular sign said that the time limit for parking there was one hour, and as a term of the contract anyone parking over this one-hour limit would have to pay a fee of $60. When Joe got out of the movie, he found a ticket on his car (a demand for payment of the $60). He refused to pay and was sued. What would be Joe's defence in these circumstances?