There is no actual difference between an Aussie and an Indonesian Harlequin Tusk except for price. Generally, the Australian fish are collected when they are larger so tend to have brighter, more deeper blues. The Indo fish tend to be collected when younger so have more of a "juvenile" coloration. Also, with the way fish are being collected now in Indonesia, the chances of getting a cyanide caught harly are far less than they used to be. Just like with any fish purchase, you want to make sure you get a good healthy fish that is eating well and doesn't appear to be stressed out (swimming, interacting, etc...). In fact, with a lot of the better distributors, Harly's from Indonesia are coming in healthier than Aussie fish simply because the shipping is faster and they spend less time sitting in bags of water in boxes now that they are improving their collection procedures.
The idea that there are spots or lines that can distinguish them is false. An Indo fish next to an Aussie fish of the same size and health will be identical.