How does adrenaline generation for the heliotrope sign work?

Solution 1:

You'll need Combat Acumen at least to build Adrenaline through sword strikes. If you only have Magical Sense, you only get Adrenaline from signs.

Make sure you have upgraded your Igni or Aard to level 3, where it affects all enemies in an area. The more enemies you manage to get in the Igni or Aard blast, the more Adrenaline you will get. Reflecting damage from Quen too build up the gauge; I haven't tried Axll or Yrden yet though.

You can also increase your Adrenaline through sword strikes if you put points in Combat Acumen (you are able to use both the Heliotrope sign and the group finisher at the same time).