The term 'WARNING TO INTRUDERS' can be summarized by two crossword solutions: NOTRE (5 letters) and NOTRESPASSING (13 letters). NOTRE is a French word meaning 'ours' or 'belonging to us'. NOTRESPASSING is a combination of the words 'not' and 'trespassing', which is an act of entering someone else's property without permission. Together, these two words form a warning to those who would enter someone else's property without permission.