and where people are being killed by some “curse” which manifests itself as a symbol on the open side of the killer’s hand…

Ok, so my post title probably describes as much as I’ll remember.  It’s vague (of course, going back to the 70’s….!) – but I think it was a British based TV series.  I remember that every episode somebody involved with the family members living in this mansion, would get killed.  It was some sort of possession by an evil spirit, that would enter somebody’s body and then the person would kill someone.  The only evidence of this “possession” was a symbol on the open side of the possessed person’s hand (you’d think a tattoo of some sort) which looked like a stylized number “7”.   Once the evil spirit would leave the person’s body… the symbol would fade away and the person would regain consciousness without having been aware of having murdered someone.    That’s all I can remember…. other than some episodes where the hired help (in the mansion, such as head-butler and maid) were possessed too.

Has anyone else seen this or aware of what this series was called ??   It’s been driving me nuts and my sister (the only other person who used to watch it with me , at that time),  has no recollection whatsoever.   Aaaaaaarghhhhh !!!

Thank you in advance if you can restore my sanity !