Australian citizens: In Australia you can either call in at your local police station and fill out a form or search on line for the term "police check" or "police clearance" followed by your State. The form and copies of proof of identity, needs to be endorsed by a JP and sent off with payment to the relevant authority. The fee is around $45 depending on which state you are in.
UK citizens: In the UK this document is known as a "basic disclosure" check. UK residents can obtain one from ‘Disclosure Scotland’, which is a government agency and covers the whole of the UK. A fee of £25 is required. http://www.disclosurescotland.co.uk/apply-online/
USA citizens: In the USA you can call in at your local police department, fill out a form and request they conduct a local or state criminal records search and provide you with a document reflecting that there is no history of a criminal record. They will let you know what else is required, such as fees and providing them with notarized proof of identity. More information can be found here: http://travel.state.gov/travel/tips/emergencies/emergencies_1201.html