I recently came across a symbol like this on a PCB: (forgive the use of Paint)

![the symbol](https://i.stack.imgur.com/jOgVC.png)

The component was marked as being 0.1 (symbol).

You can just make it out in the centre of this photo:

![the photo](https://i.stack.imgur.com/uC6jN.jpg)

It's a capacitor, so I'm guessing it's perhaps measuring farads, but surely then an F would have been used... What is it measuring?