You mean the NES mode or the hidden easter eggs that require you to cheat? If you mean the hidden easter eggs that require you to cheat, you have to press ` to open the command console (English keyboard only) then type the command ghost, which allows you to phase through walls. Explore the entire map of the first level and you'll find em both I'm sure. The first one requires you to be at second floor elevation, if you fly around you'll find the easter egg hidden on a rooftop, type the command walk to stop phase walking and get back on your feet. Here, you should be able to read the text on the sign. The second easter egg requires you to be at ground level, fly around the map and you might find the hidden text.