Can a plant be identified as either vascular or nonvascular by looking at its tissues under a microscope?

Vascular plants have vascular tissues, which circulate resources through the plant. This feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are therefore restricted to relatively small sizes.

Nonvascular plants are the simplest of all land dwelling plants. Like their closest ancestors, the green algae, they lack an internal means for water transportation. They also do not produce seeds or flowers. They generally only reach a height of one to two centimeters, because they lack the woody tissue necessary for support on land.

So to paraphrase Non vascular plants have no water system to transport water around the plant. Vascular plants have a water system.