Depends what was the intended use for the law. It's not always about enforcing it on the spot. Take another example - declaring you never joined a war on some visa applications. Of course they're not going to check that. But if it ever comes up and is discovered for some (un)related reason, you're out without further discussion.
Same can be applied here. Found to have one during some checks? You're charged.
Same can be applied here. Found to have one during some checks? You're charged.