For a website to be usable, I believe there has to be semiotics. Users need to be able to find their way around a site and without symbols and signs (semiotics), that would not be possible. If someone wants to go back a page, there's the agreed upon sign is an arrow to the left, to go forward, it's the arrow to the right. Also, to make it known that something is clickable, there will be something that tells us we can; something that differentiates the clickable items from the non-clickable. Typically a "home" button is a little house, or the name or logo of the website. All of these things are signs or symbols that let the user know where to go. It is pretty much universal.