You will see items sold here such as BOB's etc and/or a schematic posted and they all use the earth ground symbol as a power Common, regardless if it is non-earthed.
The book highly praised by many, The Art Of Electronics commit the offense all the way through.
The earth ground symbol I show was established by the JIC in the '50's.
Also there is a paper published by Siemens on the importance of equi-potential bonding in electrical enclosures etc.
It used to be available on their web site until they changed the site.
It is available by request in PDF.