I help run a model painting competition and struggled to find a good way of keeping track of models when they are being moved around for judging.  I decided to put together my own system, which includes a number attached to a paperclip with a corresponding numbered model to sit in place of the model.  The paperclip and number slot into a space underneath the number flipper for easy storage and use.

The files are designed for using small paperclips.  The print pauses so you can insert the paperclip so that it will be entirely contained in the number. 

I also inserted a small magnet to help hold the paperclip in place for extra security.  I cut strips of 12mm magnet tape to insert into the space.  The print also pauses at the appropriate place to insert the magnet.

The number flipper is designed to be pushed firmly into the paperclip holder/stand.

I did not design all of this from scratch and studied and modified several models I found freely available around the internet to achieve my vision.

I did find that one of the sets of prints I did with matte filament resulted in a very tight fit for the paperclip numbers, but the 3 other batches I printed (two silk, one matte) did not have any problems fitting together.  However, I did reduce the size of the paperclip token a smidge to reduce the likelihood of that happening. You may want to do a test of one complete model before printing everything to check the fit.