He looked very angry. 'Now you get out of here, all of you!' he shouted. 'I'm sheriff here. Do you see that notice? It says "No Camping" -- in case you can't read!'

'Look, sheriff,' said Rockwall, 'don't be too hard on us. I'm Rockwall Slinger and this is Merlin Greeves.'

'Oh, is it?' said the sheriff with a sneer. 'Well, I'm Brinksley Meers, and my other name is Gloria Gleam. Now you get out of here fast!'

为什么不是说Did you see that notice呢？用Do you 一般现在时应该是什么意思？

这里的in case 是万一的意思吗？还有就是Oh, is it ? 中的it指代的究竟是什么？