Blue Dasher (Pachydiplax longipennis) 2016-7-18 Newark, DE

Obelisk posture to prevent overheating is common in dragonflies, however, the Blue Dasher also does this to guard his territory, or to show off his blueish abdomen (mine's bluer than yours) if in conflict with another male. Since I saw two flying about but only one landed on the twig for a picture, perhaps this one was assuming the posture to ward off the other male.
https://en.wikipedia.org/wiki/Obelisk_posture