Answer
The sign in front of $\omega$ is plus.
Work Step by Step
It is given in the question that the wave is moving along a string in the negative direction of an x axis.
Therefore, the sign in front of $\omega$ is plus.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.