Struggs – you’re correct in that your Owners Corporation (O/C) cannot make changes to its Common Property without first putting its proposal/s to Owners at a General Meeting, and having those authorised by way of a Special Resolution.
Whilst Cl 65A of the NSW Strata Schemes Management Act (1996) includes a specific reference to “changes” involving the erection of structures, and your Executive Committee’s (E/C) signage would certainly be captured by that reference, Cl 65A also states the changes that require the O/C’s prior authorisation are those proposed “for the purpose of improving or enhancing the common property”, and I’m not sure that advisory signage fits that prerequisite.
As for the E/C advising the O/C of its intentions re the signage, in normal circumstances I doubt that’s necessary given it’s hardly a big-ticket item in terms of expenditure, but if there’s any relevant restriction on expenditure by the E/C or a limit (Plans >100 Lots) then yes your O/C should have been advised.
I know that the improper use of visitor parking spaces in your Plan is a long-standing problem that you’ve been trying to address with varying degrees of success, and forgive me in advance for asking this, but have you ever lodged an Application for a Compliance with By-Law Order under S138?
If you haven’t, it would certainly give your E/C Member some hurry-up and send everyone else a message; even if you only warned him that you would go in that direction!