You can specify a Creative Commons license for each board, including author attribution details. This will make it more clear to people accessing your board whether or not it is freely available for copying and redistribution. Setting an open license on your boards is a show of goodwill and encourages collaboration.
To set the license for a board, make sure you are in Edit Mode and hit "More" and then select "Edit Details".
Select a license
For the "License" option, select the Creative-Commons license you would like to apply. "CC By" requires proper attribution, "CC By-SA" requires attribution and sharing a copy of any changes. "Public domain" releases your work to the public with no restrictions. Select the license that makes the most sense to you.
Board details to see board license
You can review the license of any board when viewing it by hitting "More" and selecting "Board Details".
Review board license
You will see the license information in the window that pops up. You can also review any licenses defined for images and sounds used on the board by hitting "show additional licenses".