If you´re not planning to pay yourself any salary, then there´s no registration required.
The general information about the salary and dividends is described here, but basically if you´re a member of the Board then there are two options:
First, there is an option to register you as an employee with an employment contract. In this case there is a monthly minimum salary that needs to be paid in Estonia. You can still receive the dividends and board member fees.
The second option is the management board member service agreement. In this case there is no official minimum salary, also no unemployment security tax and therefore no protection against unemployment. The board member can have Estonian social security only if the salary is at least the official minimum salary in Estonia.
It´s very important to understand that dividends cannot be an alternative to an official salary, as dividends are not taxed with the labour taxes.