Use your key, don’t force the door
First of all, there was a time when the front door was not locked, so yeah, now people have to kinda get back to the habit of using a key. It’s a big deal! Dig well inside of your pockets, if you remember which one, if you have a spare hand, all that.
But it’s all besides the point.
Because just having such a notice on your front door says “This door can be forced. It has been forced before and you can force it right now. Keys are for sissies that stay in front of a closed door reading notices like this”