From Guild Wars Wiki
|Bonus||Armor +10 (while using a Preparation)|
A Scout's Insignia is a ranger specific upgrade component that provides an armor bonus of 10 extra armor while using a preparation. This bonus is not global and applies only to the armor piece equipped with the insignia.
|Armor +10 (while using a Preparation)|
- The description is ambiguous: you receive the armor bonus while under the effects of a preparation, not while activating one.