This image signifies a party is taking place behind the door, by recognising this you have carried out your own semiotic analysis. You deduced that the balloons on the door were a symbol of a celebration taking place, you interpretated meaning from this cobination of images (ie front door and ballons).
Semiotics reveals the ways in which people interpret everyday signs at an unconscious level to create cultural meaning – understanding semiotics gives sport organisations and brand guardians control over their cultural meaning.