Kanban style board

Kanban boards didn't originate from Toyota Production System. The signals used depended on the context. For example, the user of a part may send an empty box to the supplier as the signal. In other cases, it could have been a card. The important thing is that the consumer of whatever the thing is has a visual indicator that is sent back to the supplier when the consumer needs more.

Boards with cards on the board are often used in software development and other knowledge work because there's no boxes to put supply in or physical things to move around. The board makes it clear when one person or activity can take on more work.

Please refer Wikipedia for Kanban initiation story. And yes history suggest that Kanban iniatation from Toyota.

Its basically to visualize workflow, optimize the workflow using WIP limits.

Few good articles -

Kanban Board: Basics, Features and How to Use it (kanbanize.com)

Kanban - A brief introduction | Atlassian

if this is true, does it mean that we are using Kanban as the sign system in Scrum? As "Kanban" in itself means "sign".

Not really, because Kanban is systemically about far more than signs. Systemically it is a closed economic model of production subject to conservation of flow.

In Scrum it is possible to use a Kanban system as a strategy for implementing the framework. The "sign system" you refer to (a board) might be a visualization of a workflow being managed according to such policies.

It's possible to use something like a Kanban board as a pure information radiator which signals various things. Doing so can be advantageous for building transparency, but without policies to act on them, a Kanban system won't be achieved.