I saw another maker's version of a magnetic mailbox indicator on r/functionalprint. I immediately thought that was something I needed, but I wanted a simpler version. This design is two parts that snap fit into one another and work via mechanical/gravity interactions only (non-magnetic). I printed the two parts on my Makerbot Replicator using a black PLA and a white PLA at 0.3mm layer heights, 3 perimeters, 25% infill, no supports.

GIF of it in action:

[https://media.giphy.com/media/lGv0XKuv4JISVoHssw/giphy-downsized-large.gif](https://media.giphy.com/media/lGv0XKuv4JISVoHssw/giphy-downsized-large.gif)