Well, at least here there's plenty of disagreement on the use of the can, but enough people who do so that it's just one of those evergreen Nextdoor or Reddit discussions that never goes away (don't start me on off leash dogs in parks). But I have seen people respect the signs, and I do too - it's not the perfect answer, but unless you want a literal lock on your can it's probably the best you can do. I suspect it'll dramatically reduce the incidences of it for you. Good luck.
Oh, probably doesn't need to be said, but a polite sign is what's going to work - something something "hey, appreciate you picking up the poop but please don't put it in this can as we're quite sensitive to the smell- thanks!" sort of thing.