I know it for sure

I highly believe it is Bobby. Who else would be willing to stick around and help out with cleaning up the place and happening to give the boys "hints"? It is for sure Bobby :)

i wish its him... hell i miss ya Bobby!!

It must be Bobby; who or what else could it be? Even death can't prevent him from looking after his boys.

Also, I think the writers pretty much flat-out confirmed in an interview that Bobby isn't truly gone.

I figured the ghost-y stuff was either Cas or Bobby. It's obviously not Cas...

Of course!

i hope and pray