Which method is linked to potential terrorist financing according to the provided information?

The method associated with potential terrorist financing is utilizing post office boxes instead of permanent addresses. This practice can raise red flags because it allows individuals to obscure their true identity and address, making it challenging for authorities to track their financial activities. Such anonymity can facilitate illegal operations, as it may prevent law enforcement from conducting thorough background checks or tracing transactions back to an individual.

Using mobile banking apps, making electronic payments, and investing in fixed deposits typically involve more transparency and traceability in financial activities, making them less commonly linked to terrorist financing activities. In contrast, the use of post office boxes could suggest an intention to avoid detection.