Passwords with non-alphabetic or non-numeric characters

Hey, I saw this page: http://www.freepbx.org/support/documentation/faq/changing-the-asterisk-manager-password

and it says not to use non-alphabetic or non-numeric characters for asterisk manager.

There’s any other password I need to be careful not to use symbols? I afraid to break my system so I’m not trying, but I really prefer to use symbols to harden the passwords in my system.

Thank you!