On every sign I destroy, I get the message "The leaderboard was removed".
I don't want every sign to be a leaderboard.

I can not reproduce this problem. It does not happen on my test server. I need more information to solve your issue.

Do you get any errors in the console?

Any errors in your log when you start the server?

try enable debug information before you destoy a sign using "/mh debug" and check the console for information, after destroying the sign

No errors. I will try /mh debug.

do you still have problems with the leaderboards?

I can confirm that I have this problem as well.
It happened after I created a leaderboard in my Survival world.
Every sign that is attached to a wall, that I break now gives me the same message 'The leaderboard was removed'. It is kind of annoying haha.
The command I used was: "/mh leaderboard create Total_Kills AllTime".
The leaderboard by the way works just fine.

fixed in next release

Problem identified. I will see if I have time to fix this tonight.

Released