What do the line-and-circle symbols mean on these electric meters?
Below are my interpretations of the various symbols.  I included more than just the line-and-circle symbols, for the benefit of future visitors:
50 Hz AC:

Double Insulated:

Non-reversing (not suitable for power export or net-metering):

CE Marking (meets European Community standards):

Three-phase Wye:

Single-phase plus grounded neutral:

Single-phase ungrounded:

Single phase with center tap neutral:

Two phases of 3-phase system, plus neutral (This would give you 230V from phase to neutral, or 400V between phases, but no three-phase):

Corner-grounded 3-phase open delta:

Quadrature (phases 90° apart):

Contains lithium battery (probably for backup or to power a communications device):