My dog nurses on a teddy bear. Is this a sign of anything?

It's completely normal. There is no one cause for the behavior, but I've owned and worked with TONS of dogs who do this. My male Doberman makes me Doberlace from his blankets and "nurses" on all his stuffed toys. My female Pit does the same, we never leave important blankets, sheets etc. around her because she "nurses" holes all through them.