I saw someone posting a interesting theory about this online, the person was saying that this is the music name, that probably was used in 319 when Neal send the warning to Hook and that Mark keeps re- using old songs from past seasons, since no more soundtracks from the show were released, so this is just the song name, because Mark would not change the song title ,
Yes I was thinking something along the same lines. We know that Mark reuses music and musical cues during certain scenes (the Evil Queen’s menacing music, the Rumbelle music); little hints that that invoke the past. It’s very possible that Mark is just reusing some music and his hand was slapped (by A and E or by ABC) not because MRJ is actually coming back (or because they are going to use Neal again) but because showing that picture on Instagram makes it LOOK like they are going to and that causes an uproar.