permissionstrello
How to prevent someone adding me to a board without my permission?
There is no 'report abuse' link in the email which informs me someone has added me to a group without my permission.
There are only links to more spam, and trello preferences. It is a genuine email from Trello, the spam link is what Trello provides (eg 6 ways to get more out of Trello etc etc etc)
Why does Trello allow this?
No, there currently is no way to do this. Permissions is something we may add later and I assume that it would be covered by that, but we don't have any time frame on when that might happen (and we might also charge for features like that).
As I always wanted this feature, I wrote a bot that keeps cards in sync across Boards.
See if it suits your needs. From the description:
Hello, my name is cardsync and I am a bot designed to keep cards in sync, which means I update the content of one Trello card to reflect changes made on other card.
Also, here's a small gif animation that shows it in action:
Best Answer
Unfortunately, Trello doesn't provide a option to prevent being added into a board.
But they have a "Report Abuse" thing:
They should respond rather quickly.