Just so I'm clear you clicked your little user head icon in the top right corner right below the navigation bar and clicked preferences right and then went to signature settings?
If changing it there doesn't work you might have to do it the old way. Click the button that says 'my account' in the very top right corner and right next to your avatar to the right click 'change my avatar' or whatever and below there is another space to clear you signature although the first way I mentioned should work.
Re: Help pls- I can't get rid of my old tickers.