Chris Lamb "..indicate by the manner of my delivery that the song has ended, for example by increasing the volume..."

Yes, or lengthening of the last note(not sure about vibrato though, personally) or a nod of the head, / smile...

It's quite embarrassing as an an audience member when I don't know if the song has ended. It's good to get a clear indication.
I actually like it when there is a second of silence at the end of a piece. I really hate people clapping in the final moments of the song. I want the silence to be part of the performance.