What is the correct schematic symbol to use for virtual ground?
I wouldn't use the "earth" symbol unless I meant mains earth or Earth.

There are various ground symbols available.



Figure 1. From Ground, earth and chassis explained (by me).

In your case I would probably use the hollow ground symbol for the real ground and the solid ground symbol for the virtual ground.



Figure 2. Different ground symbols for primary ground and virtual ground.

Notes:


R1 and 2 provide a VCC/2 reference.
C1 stabilises the reference voltage and keeps it constant during fluctuations in VCC.
U1 provides the virtual ground.
C2 is the supply decoupling capacitor for the op-amp.




From the comments:


  The opamp is just a voltage follower? Why call Vcc/2 virtual ground?


Virtual ground appears to have several meanings. In the inverting amplifier op-amp configuration it refers to the inverting input as being very close to ground potential due to the high gain and negative feedback. In this case of Figure 2, below, and the OP's question it is a ground or reference for the audio signals and they alternate above and below that reference voltage and are equal to that reference voltage when the audio is quiescent.

The term seems to have high-level approval. See TI's datasheet for TLE2426, The "Rail Splitter precision virtual ground" device.



Figure 3. The Belton-Brick uses a virtual ground reference, VB, for biasing all all the op-amps in the audio signal chain to half-supply to allow for alternating audio voltages. (Double-click for high resolution.) Source: Hot Bottles.