Just reading body language, this is what I get out of this picture:
Grace: "Luke, can you read what that sign says?"
Luke: "I don't know how to read, you're the oldest here, can't you read it?"
Grace: "No, I have no idea what it says."
Luke: "Well, you know what I always say: If you can't read it, you don't have to obey it! Hey Silas, throw us the key!"
And what will they plead if arrested for trespassing? Nolo Comprehende?