Dear @peniwize, I am not aware of direct entry of special symbols in QLineEdit in MAC but in WINDOWS OS we can do with the help of ALT key and the symbol code. Basically go to Character Map and select the special symbol then you will be able to see the corresponding Key code to that special character. Just hold ALT symbol and enter the code from num pad by enabling NUM LOCK. Then release the ALT key. That special symbol will automatically appear in the QLineEdit in Windows. May be something similar you can try in MAC OS too.
Good luck!!