The strap hangers are designed for male commuters to have something in their hands, so that they're not accused of groping women on the subway!
Apparently the straps which retail at 525 yen (about two pounds fifty) are selling like hot cakes. Groping is such a common occcurance in Tokyo that men feel the need to make it clear they have something else in their hands. What's wrong with a book or a newspaper?
I happened to be watching The Best of The Graham Norton Show last week and caught the actress Miriam Margolyes telling a story about how she once had a man pressing his erection in her back when she was on the Tube. Being Miriam Margolyes, she didn't keep quiet about it and managed to embarrass him in front of the whole carriage.
An old colleague of mine also has a dinner party story where a man put his hand on her derrière on the Tube. She lifted it up and said loudly, "Does anyone know who this belongs to? As it seems to have become attached to my arse?"
Fortunately that's about as much as I've heard about London Underground groping or the likes recently. So either it doesn't happen much or no one talks about it. Let's hope it's the former.