A coin drops at a known speed and the right coin will get pulled by the right amount by a magnet or get rejected.
If you have a silver coin or a small piece of copper pipe and a large, strong neodymium magnet, then you can easily observe this effect at home by putting the metal sample on a table and quickly waving the magnet past it as close as you can without touching it. The metal will slide across the table following the magnet, despite the metal itself not being magnetic, because the moving magnet induces eddy currents which temporarily create a magnetic field like an electromagnet. Other metals besides silver and copper exhibit weaker responses due to higher electrical resistivity.
Otoh, there are coin mechanisms that can check for and reject quarter sized objects that are attracted to magnets; they might not be installed everywhere that takes US quarters, but if an operator starts getting a nuisance amount of CA quarters, they will be. See this doc [1] for a description of a pretty discerning mechanism (although it accepts both US and CA quarters, a slightly different design could reject CA quarters)
[1] http://segalandassociates.com/Documents/Coin-Mechanisms_Slug...
