I have written this in multiple posts but I might as well write it once more.
1. Go to User CP -> Edit signature
2. Open Windows Notepad
3. Go back to the site and copy the text you have in your signature
4. Paste it into Notepad
5. Delete the text from your signature
6. Click OK and save changes
7. Click Edit Signature and start pasting the text you have in Notepad line by line, saving it each time
8. When it starts complaining you see where the problem is.