The lines are pretty recognizable as drag handles (in lists, on windows, etc), but to be honest I never dragged that icon in Facebook until you mentioned it. In

The lines are pretty recognizable as drag handles (in lists, on windows, etc), but to be honest I never dragged that icon in Facebook until you mentioned it. In a button, they do not look like drag handles. On the iOS keyboard, one thing that makes them instantly readable is their physicality (they're embossed), which communicates 'grip'. The grip concept goes back even further, to the classic Mac OS look.