So without a warning, it would be difficult for most of us to realize that this patch had been added.
Before you can see the warning, you would have clicked on the lock thread to see it. If you click on the locked thread, you will see the quote icon. The quote icon was not there before beside merit icon but it is there now which is enough.The quote icon edges is in faded blue colour which is different from the usual blue colour.
How many closed topics have you visited today? I haven't visited any today...
If there was no warning, you would only notice this when you enter a closed topic and stay there long enough to notice that button is available.
Unless you are a user very used to visiting a closed topic, it would take some time to notice the difference. We are used to seeing this button on all posts, and even though it has slight graphical differences, you wouldn't notice it the first time you pass by it, as you are used to seeing this button. Therefore, it makes sense that this alert/information was made.