Loving this image I just discovered via Nikki Brittain. It reads “Things Aren’t Always #000000 and #FFFFFF”, which are the computer equivalents of Black and White. Original stuff!
Go Away / Come In household door mat. I think this is great, with some unique typographic treatment that makes the design work. When someone enters a house, the doormat reads ‘Come in’, yet it appears to say ‘Go away’ when the visitor leaves.