Your signature is too long, try to shorten it [;)]

That would be a serious flaw in the forum code. User input should always be verified before passing to a SQL query. Unfortunately the forum code is very, very old so nothing can be done about that.

Just checked the input form. You could enter a whole book in the textarea [:))]
Of course that can't be stored in the database, the textarea should have limited the number of characters to what can be stored.

... Checking the page source confirms the flaw: the textarea is missing That's a beginners mistake.