Sometimes it makes sense to be able to move a button from one place to another – possibly change its use from function to decorative and then back to function again – and this is one way of giving a button roving status. 

A sturdy linen yarn is threaded through the holes….

…. and knotted a few times on the back of the button.

Here it is attached to a vest by catching those knots in the back of the vest with that most wonderful of invention – the safety pin.

Purely decorative,  this 'button by Bob' goes traveling on a hat.

The pinned side.