A charge sign can be assigned to the following type of groups:
During group creation, you have the option to display the charge on the charged atom itself or the whole group.
In the latter case, the charge is displayed outside of the bracket on the right.
If any additional charges are added, the net charge will be calculated and displayed.
The charge-bearing atom can be revealed by pointing the cursor over the group (in select mode).
To replace the charge, select the group and navigate Structure > Group > Edit Group (or right-click the selected group, and select Edit Group).