I have purchased the bottom half of a head on ebay. For display purposes - as you can see in the photo below, the head has an ear which has a hole so you can display earrings. It's a hassle to show the relative size of earrings in photos. It's not good to use a coin, because it's country specific, so will mean nothing to people unfamiliar with British money. A ruler looks a bit naff and personally I don't think it helps if you've already stated measurements in your description. Bits of food don't look so good, etc. (I've been using a thimble, which is ok but then I suppose there are loads of people who don't use thimbles plus I think thimble size can vary...?) So I got this head and I'm hoping it's going to solve this issue!!
I've never bought anything off ebay before, only sold things on it. So I'm hoping that this head arrives soon. The seller had a very good rating - sold about a trillion items and 100% positive feedback. So maybe today in the post???!!