They were super simple. All you need is some brown craft foam, binkies and glue.
Step 1: Print out mustache shapes from the internet and trace them onto the craft foam
Step 2: Cut out mustaches
Step 3: Glue them to the front of the binky.
Kaypha is nearing the end of his use of the binky (hopefully!) but I made one for him using an old binky so he could model it for us: