As others hae said, searches only currently work on keywords, and keywords are a rocky area in the App Store. The keyword guidance states:
"The most common rejections are for keywords which are offensive, objectionable words or phrases; using trademarks, company or product names"
The SOF trademark page states
"The Stack Overflow and Stack Exchange name and logos are trademarks of Stack Overflow Inc. The names and logos for sites and products operating on the Stack Exchange network are also trademarks of Stack Overflow Inc."
Now, it also says it's generally OK to use the name, but don't explicitly say "You can use the names in advertising" (though I'm sure that's what was meant, as long as it doesn't appear to be an endorsement). As we know, the App Store reviewers are not very nuanced and I really didn't want a rejection fight or post-release pull off for Six to Eight v1.0, so I was quite conservative (this also explains the 17+ age rating). They're also not consistent, so the fact that other apps already used them is no defence in their eyes.
I've a version with a few minor bug fixes coming, and I plan to use that to drop the age rating, add the keywords and have any arguments that might result. They're sometimes easier on updates, and I can give more explanation in my review notes to explain (there was limited space left for 1.0).