On a few of my tunes, a red square within a red circle has appeared after having used them multiple times, what does it mean?

On some of my tunes within iTunes on my ipad Mini, a red square within a red circle has appeared after having played them multiple times. I have deleted them on the ipad, and done a sync with my computer, (the tunes are actually still on the computer,) but they have not reappeared. I now do not know what to do to get them on my ipad Mini. ????