I remember something like that. It was like a butler creek cover for the eyepiece and had yellow pointers supposedly to center your eye on the scope. I seem to recall a bit of a debate amongst the local HFT crowd as to the legality of them. Oh how us normal folk laughed........
Accuview keeps springing to mind but I cant quite remember.
Edit: Thanks Wil95k, I would have spent all night wondering about that....