To be precise: appending "[small, no ads]", "[no ads]" or "[without ads]" to the play store app title causes a rejection. I didn't want to test more in fear of banning, and in the end removed it. I know you can see if an app contains ads in the app page, but not in the search results... or at least not yet, but I doubt Google will add that indication.
[1] https://support.google.com/googleplay/android-developer/answ...