Available at Target, of all places.
I’m pretty sure that these doormats provide independent probable cause for entry into the residence.
P.S. If you choose to purchase the doormat, make sure you are abreast of the most recent Supreme Court case law. As of today, police officers who take up your doormat’s suggestion may not be doing too much knocking and announcing when they return with that warrant. They’re still supposed to — but if they don’t, the evidence they seize won’t be suppressed at your trial. So you might want to go ahead and dispose of your contraband now.