Some of the legal issues associated with motor accidents occuring on private property were brought out on the last episode of “Four Corners” entitled “While they were sleeping”. In NSW at least, it seems that police powers to prosecute drivers on private land are limited. This program is currently still available on i-view and I found it to be well worth watching.
Whilst speed limit signs are virtually impossible to enforce on strata property, at least they give a reminder to owners and visitors what is reasonably expected. If you have a persistent offender it is possible to estimate their average speeds over a known distance by using a stopwatch.