This app was mentioned in 4 comments, with an average of 3.00 upvotes
There is an app called monitor that sends you a notification any time a word you set as a keyword is used on Reddit. I can see how this could actually be useful for a lot of things.
This should do the trick but it monitors the whole of Reddit instead of localizing it to a particular sub Reddit. You could email the dev and ask him to add that as a feature though.
This app monitors reddit for specific terms and keywords. It only shows the partular post with the searc term or keyword (I.e not the whole thread) so it might be what you need.
https://play.google.com/store/apps/details?id=smugcat93.monitorforreddit
Search the top posts of the month, an app was mentioned that does just that.
Edit: https://play.google.com/store/apps/details?id=smugcat93.monitorforreddit