I usually have a pack of origami paper in my bag when I'm on my travels.
If I spot commuters and travellers who use tickets or dogears to mark their places in a book, I take out my paper and fold them a little origami bookmark.
I get some strange looks at first as I place the folded paper on the corner of their page.
But that soon changes to realisation and a smile.
So if a woman puts a coloured piece of paper on the corner of your page one day ~
it will probably be me, the guerilla bookmark giver.