mobile

So I rooted my phone sometime ago and now I want to unroot it. I went through the SuperUser to unroot and it deleted SuperUser after it was "done". I installed a root checker and it said it was unrooted.
But when I restart my phone it still has the Custom lock key on there. Is there any way I can get it to remove that symbol?
Even though my device has that symbol is it still unrooted?

I even factory reset my phone and it was still there so I am running out of options. PLEASE HELP!

Thanks!