Miggie is the Afrikaans word for midge. I’m not sure whether the sign is suggesting cow-dung will find its way up your nose along with the midges, but it does seem to imply that this kind of experience is something you might want to be reminded of when looking at the paint on your patio floor.
If you think I’ve found references to cow dung and miggies in Edinburgh, I’m sorry to disappoint you. This is a rather old photo I found on my mobile.
The Waffle Group 
Perhaps you can be the first to introduce nostril miggies to Edinburgh. It might be a big hit?
Failing that, a subplot for Commitment Man?
Always a safe bet.