In case your detail level in a Card's or Board's stream is set to Relevant or Comments, you will see the full-text message of the most important actions and icons indicating less important actions. This guide will show you the meaning of the icons.
See the example here - in this card, the detail level is set to Comments. All actions besides messages are indicated by icons.
In the case when there is a numeric value before the icon, it means that the action was done a number of times. In the example below, users were set to be responsible 4 times.
Guide for icons
A card was created by some user.
A card was copied from another card.
A card was archived.
A person was made responsible.
A date was removed from a card.
A label was added or removed from a card.
A relation (Parent, Child, Next, Previous) was added or removed from a card.
A status was changed.
Content in a Note was changed.
A Todo item was marked as completed.
Customer support service by UserEcho