This below link describes both 150n and 50s life jackets. That should help?
Read more at http://www.mysailing.com.au/news/choosing-the-right-pfd#gQkf3WQQfDs1zdP4.99
Here is a good write up about the life jackets in Randwick
http://www.watersafety.nsw.gov.au/Pages/Rock-fishing/lifejacket-law.aspx
fines only started in June this year, so they must be enforcing it now!