My layman's understanding of trademarks is that the salient detail is whether your use of the trademark would likely cause confusion about the source of the mat

My layman's understanding of trademarks is that the salient detail is whether your use of the trademark would likely cause confusion about the source of the material. The question then is if your app showing up for search results (or whatever other side effects might happen from your use of the trademark) about scrabble would be likely to convince people that the app _might be_ officially endorsed. I believe current US case law is trending toward keyword stuffing not generally being a trademark violation, even when explicitly targeting a trademarked competitor, but people are getting dragged to court over it from time to time, so that might be more than you'd like to take on.