No trespassing sign
A no trespassing sign was a sign that warned would-be trespassers that they were not welcome.
In 2152, when Malcolm Reed expressed misgivings about "snooping around" the automated repair station, Trip Tucker replied, "I haven't seen any no trespassing signs." (ENT: "Dead Stop")
Also that year, Jonathan Archer mentioned that the Tandarans might consider putting up a "no trespassing" sign when he and Travis Mayweather were caught violating Tandaran territory. (ENT: "Detained")