The format for S7 tags is in the Ignition manual. The ET200S behaves like a standard S7-1500, so A0.0 is QX0.0 in Ignition, DB300.DBX0.0 is DB300,X0.0
Note that Ignition’s Siemens driver has no support for symbolic addressing, so you have to disable optimized access for data blocks you want to access from Ignition.
For the safety part: I really hope you are not planning to interact directly with safety data blocks from your HMI. There are rules what data can be accessed from the non-safe part of the application, those rules also apply for HMI access.
The password protection for F-blocks is a safety feature to prevent changes to safety functions. But why should you want to change the safety program from your HMI?