"The sensors are set to search for life signs."
Translation:yInroH lunejbeH nochmey.
yInroH nejbeH nochmey. was not accepted, as it's missing the lu- before the verb.
But is yInroH really grammatically singular and refering to the English plural life signs? Can't we speak of wa' yInroH and cha' yInroH(mey) and yInroH(mey) law'? With the plural being optional, also the lu- wouldn't be necessary. What do you think?
I believe that it's a mass noun in Klingon, and that the English translation with a plural is due to how English works.
A bit like "furniture" which becomes plural "Möbel" in German, or "Gemüse" which becomes plural "vegetables" in English, or even "information" in English which becomes plural "Informationen" in German.
You can't have "three informations" and I believe you can't have wej yInroHmey -- you detect an uncountable mass of yInroH much as a wiki contains an uncountable mass of "information".
In most cases, you could probably use either. nej focuses on the the search without reference to the finding. Sam focuses on the end result of finding the thing. Of course, no one would ever nej without hoping to Sam. If you are talking about what you are doing now or will be doing in the future, they're probably fairly equivalent. But if you are talking about the past, there is a heavy implication in nej that it may not have been found, or at least that the finding is not important to the story you are telling.