Semiotics, in brief, is the study of how we construct meaning. For example the phrase ‘green light’ has a meaning beyond a literal green light – it can be used metaphorically as giving permission to go ahead. Even if you’re not familiar with them, you won’t be surprised to learn that the Lorde song Green Light and the Ting Tings song Traffic Light are not about literal lights.
Ferdinand de Saussure wrote about the relationship between a ‘signifier’ and ‘signified’ – the sign and the thing it represents. So a nuclear waste sign is not dangerous itself, but signifies that radioactive material is inside a container, or nearby. Similarly a lit green light is associated with the abstract concept of going, and a red light with the abstract concept of stopping.
Semiotics can be confusing – I’ve studied it at university level and still find a lot of de Saussure and Roland Barthes mind-bending – but it’s a process that almost all of us have a basic understanding of on a subconscious level. We make sense of these signifiers on a daily basis without really thinking about it.