MLAK stands for Master Locksmiths Access Key.
The key system has been adopted by many organizations, including Councils. They are used in public areas of facilities, often found on gates around accessible Liberty Swings in playgrounds and other areas where people with disabilities can access at any time they wish.
Councils typically provide these keys for free to community members. Alternatively, the keys can only be purchased from the Master Locksmiths Association of Australia and those wishing to get one can only do so with written authority from their doctor, a disability organisation or a community health centre.
Further information on MLAK & Toilets can be obtained here: http://www.masterlocksmiths.com.au/mlak.php