It is for EXTRA PROTECTION. And based on the survey I filled in, keeping the string clean.

That's not sad or creepy! I think highly of you for it. Our local organic co-op stocks the mooncup, but I haven't checked to see if Boots do. My mum once tried to tell me what a funny conversation she'd been having with a friend that ended abruptly when she said "have you heard of a mooncup</i" and I sad "yes, I have one", and she stopped talking.