If you have a pet, you've probably experienced them begging for a meal when you're “positive” they have already eaten. If you're not using your smart/cell/mobile phone to track such things, this could be a useful model for you. Of course, it only works for pets that get two feedings per day.
The single magnet is 12mmx3mm, which I got from Amazon.
The check mark indicator is held in place by friction. You may need to scale the check model up or down by 1% or so in your slicer to make it fit snugly.
If you have a single filament printer, you could insert a pause to change filament at a specific layer to achieve better legibility (see photos).
Since the two models have slightly different heights, if you are doing a manual color change, you should probably print the models one at a time.
I printed mine with white PLA and transparent red on an original Ender-3 about two years ago. No supports should be required, although if your printer doesn't handle bridging well, you might need to consider using supports for the magnet indent.
The author marked this model as their own original creation.