A simple Hammer and Sickle fridge magnet. There is a void in the middle of the magnet which can fit a 30x10x5 mm magnet, like the ones found here: https://www.amazon.com/gp/product/B09M6SN3XF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

If you insert a pause into the G-code at the correct spot, you can pop the magnet in mid-print and it will be totally encapsulated. I recommend using bright, shiny filament. 

Happy printing, comrades!