This depends on the type of sign proposed and what the category of sign applies. Each category of sign has a number of sign types that do not require a planning permit provided certain conditions are met.
In Commercial zones, for example, which are Category 1 signs, business identification and promotion signs with a total display area of 8 square metres or less, including up to 1.5 metres of internally illuminated signage, do not require a permit.
In Industrial zones, which are Category 2 signs, business identification and promotion signs with a total display area of 8 square metres or less, including up to 1.5 metres of internally illuminated signage, do not require a permit, provided any internally illuminates signage is more than 30 metres from a residential zone or pedestrian or traffic lights.
Business identification signs in Category 4, which is for Sensitive Areas, with a total display area of 3 square metres or less, require a permit and are prohibited from being larger. Internally illuminated signage requires a permit and is only permissible on land used for a Freeway service centre or Service station.
You do not need a planning permit to update or replace existing signage provided:
That is, updating existing signage is exempt from requiring a planning permit provided it meets the conditions above.
There are also types of signs that are specifically exempted from requiring a planning permit. This includes a sign inside a building that cannot generally be seen outside. Here is a full list of specific types of signs not requiring a permit.