The erection of advertising or signage can often be undertaken as exempt development (development which does not require consent via a DA) or complying development (via a Complying Development Certificate) under State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 (Codes SEPP).
The NSW Department of Planning and Environment has prepared a useful fact sheet which outlines the circumstances in which signage can be undertaken as exempt or complying development. If your proposed signage does not satisfy these requirements, a Development Application (DA) is required.
See further guidance on DA lodgement requirements using Council’s DA Matrix and Plan and Report Guide here: The DA Process - Your guide