The type of electroscope that can be recognized to be charged just by observation is a leaf electroscope.

Here's why:

* Leaf Electroscope Design: It consists of two thin, lightweight metal leaves attached to a metal rod. The rod is connected to a metal knob at the top.

* How it Works: When the electroscope is charged, the leaves acquire the same charge. Since like charges repel, the leaves will spread apart.

* Observation: The degree to which the leaves spread apart indicates the amount of charge. You can see the leaves move, even without any measuring instruments.

Let me know if you'd like more details on how electroscopes work!