In the comments to Orin Kerr's recent post on the origins of the folk belief that undercover cops must identify themselves, this squib caught my eye:
There is a folk belief, certainly related, that the owner or occupier of property may post a sign requiring law-enforcement personnel to identify themselves upon entry, and they must comply even if undercover. I've seen professional-looking signs to this effect at fraternity houses.At the risk of sounding silly (it's been a while since crim pro): what's wrong with this? If I post a sign on my land that states that hikers may enter but hunters must obtain permission before doing so, wouldn't any hunter who snuck in be a trespasser? An undercover cop seeking to enter a home is presumably looking for evidence of criminal activity that could not be seen from outside the home. If the evidence is not in plain view and circumstances do not justify a warrantless search, wouldn't his unannounced entry similarly be unlawful trespassing, justifying exclusion of any fruits of the search?
Making access to your property conditional seems fairly fundamental.