If you have neutral trust, you can join any signature campaign. But it's a better option to have positive trust than neutral trust.
Correct. Positive or Neutral trust is allowed to join a signature campaign. While negative trust is mostly not allowed. It makes sense if accounts with negative trust are ignored from signature campaign participation since they have bad behavior.
After a long time I am back here to see that whats going on here in this forum .
Welcome back, mate. Now you are better to focus on improving the number and quality of your posts. Don't think too much about trust, gaining Merit is more important than having positive trust.
Read this one : https://bitcointalk.org/index.php?topic=2766177.0