Thomas A Sebeok describes Semiotics as "The study of the difference between illusion and reality"; how we differentiate between living things and inanimate objects. Semiotics is the theory of signs, informing the reader of its purpose through an illustrative medium. However signs only signify a meaning when we attach a meaning to it. If we agree upon its significance it can mean anything we like and can take on multiple interpretations, for example the image of a hand - stop, hello, goodbye, hi 5, ect.
In this case it represents stop, this is due to the context in which the hand is surrounded. The colour red connotes danger, and therefore is likely to mean an order or instruction rather than a friendly gesture.
Due to the prevalence of signage we tend to unconsciously associate them to cultural conventions. The linguist Ferdinand de Saussure invented a model which describes the composites/ elements of a sign. "He defined a sign as being composed of: a 'signifier' (signifiant) - the form which the sign takes;
and - the 'signified' (signifié) - the concept it represents." e.g. disabled access
sign = signified + signifier; the associations of the two parts is what provides our understanding.
There are 3 types of signs; the first is an Iconic sign which has a direct implication it simply describes what it represents. An example of this would be the disabled symbol as seen as above, it looks like a person sat down on a wheel - which would therefore connote a wheelchair which is associated with disabilities.
2nd - Indexical - The signified and the signifier have a causal relationship, an example of this would be the infamous peace symbol. This was designed by Gerald Holtom a member of the campaign for nuclear disarm of which the symbol originated. The design employs naval semaphore of the two letters N and D (nuclear disarmament). The N is displayed using two flags, each pointing down at a forty five degree angle, and the D is again two flags but this time with both arms outstretched one straight up and one straight down. The semaphores are supposedly upside down, i.e. the D is over the N which stands for anti-miltary.
This symbol was quickly adopted in the US and its power was reinforced through usage in civil rights marches, it was also strongly opposed by fundamentalist organisations.
The design is one of the most widely recognised signs in the world.
3rd - Arbitrary - The sign has no relation to what it refers to, (double yellow lines) neither direct or indexical. When using arbitrary signs we have to know the person were communicating with understands the same meaning. This type of sign relies exclusively on the reader having learnt this meaning.
These two symbols would be completly lost on someone who has no understanding of astrology. Each represent Mars or Venus the concept of men and women are from different planets. This notion is widely understood in somewhere like Britain where we are rich in diverse cultures. Remote destinations may not acknowledge existence of other planets and their individual relation to behavior. Therefore using this sign as a way of communicating your gender or beliefs will not be recognized.
When designing it is important to consider semiotics to ensure the message you are communicating will be correctly interpreted. Signs are entirely dependant on their context, without which we have no undersatnding for what they imply.