You can add members or groups of members to the card in order to receive notifications if something changes in it.
Open the card and click on the "Add participants" link. In the window that appears, select the person or group you need
Click on the participant's avatar in the card. In the window that appears, click "Remove from card"
There are 3 roles for members of card:
3. responsible member
You become card's owner upon it's creation.
Everyone who was added to the card as members
There can be only one person in charge of the card. To appoint a person in charge, you need to click on the participant's avatar. In the window that appears, click "Make responsible".
If card is created in columns with type “In progress” or “Done”, person who did this automatically becomes responsible member of a card.
If card is moved by someone, person is added a card. If no members exist by the time of first movement, person becomes responsible as well.