The male Variable Damselfly has a distinctive "wine glass" marking on the second segment of the abdomen.
This is a black U-shaped mark with a black line joining the segment's narrow terminal black band.
This distinguishes it from the Azure Damselfly (Coenagrion puella) which has the U-shape but no line connecting it to the terminal band.

1st photo: 's Graveland, The Netherlands, 13 June 2012
2nd photo: Naardermeer, The Netherlands, 2 May 2015
3rd photo: Zanderij Crailo, Hilversum, The Netherlands, 24 June 2013
4th photo: Naardermeer, The Netherlands, 26 April 2014