This is what I wrote back in 2010:
<<<<We use turkey wing tags at birth to identify the lambs - Soay and Hebridean. They are tiny with 3 numbers on and look like a tiny padlock. The wire loop is just pushed through the ear then clicked shut, so mimimal trauma. They do occasionally lose one but it's not a major problem. Then at 4 months ie weaning we swap for the bigger permanent tags and cross-ref the numbers. The tags come from Roxan and can be re-used if you clean them. This year our Soays are a variety of colours and we can tell them all apart so we didn't bother with the turkey wing tags.>>>>
This is the link
http://www.tagfaster.com/padlock-startin-tags-61-p.asp I suppose they must be made by 'tagfaster' and are sold through roxan. They come in 4 colours, numbers of your choice. You're not supposed to tell them they're for sheep........ just suddenly become a turkey owner for the day.
BUT you can't see them from a distance, other than to see they are wearing them. We leave them until the lambs are 4 months when we put in the Bubblegum tags. A few will have lost their little tags by then, but you can still sort them out by the 'see who baa's at which lamb' method.
I love the idea of luminous paint - you could put it on their toes
. Once they have horns of course you can use various colours of electrical tape, but no use for lambs.
Or, if you keep topknot sheep you could tie a coloured ribbon in that - not sure how long it would stay in place. I suppose that could work on fleece anywhere. I don't like things tied around their necks though.