What does the southern cross tattoo mean?

It's a symbol of nationalism. The Southern Cross appears on the Australian flag and it is a mark of respect to your country and pride from where you have come from. It is a way of associating with your heritage and is the most visible star formation known to Australians.

It is also a symbol of rebellion. It was first used in this form at Ballarat in 1854 by the gold diggers during The Eureka rebellion. The Eureka rebellion was led by Peter Lalor and was a short lived revolt against petty officialdom and although a military failure, led to political and personal benefits for many Australians.