I'm from vic, Mmm pretty sure its a public indecent thing.
I was looking around for an answer too, Um haven't been caught as yet :)
Best I can find is: A person who, in a public place or while visible from a public place or from occupied premises, wilfully does a grossly indecent act, whether alone or with another person, is guilty of an offence and liable to a penalty of a maximum fine of $2500 or imprisonment for six months [Summary Offences Act 1953 s.23].
Indecent is more of a circumstances thing, i read somewhere a lady got fined for sunbathing naked in her backyard which is kinda odd
A person who behaves in an indecent manner in a public place, or while visible from a public place or in a police station is guilty of an offence punished by a fine of up to $1250 or three months imprisonment [Summary Offences Act 1953 s.23].
Hope that helps ya, its alittle confusing