I keep seeing puppies in the nest with coloured collars on for identification
any forum readers used these, I have previously used nail polish but its not very good.

I used coloured ribbons on my litter with an easy break on incase they got caught. They looked really good! (I think theres pics on here somewhere)

You can buy 'proper' ones that are like the wrist bands you get in hospital but in my opinion, ribbon is just as effective and easy to replace for lost/chewed ones.

Look on ebay they do packs of theese and they are very cheep to buy.