They didn't "officially" signal it because it had been ruled a TD and not a fumble, but the refs on the field did tell the Miami players they had recovered. They took the ball from the Miami player and told the players that they had recovered, but that it had been ruled a TD before the fumble so it didn't matter who recovered. Once the play was challenged according to instant replay rules you have to be able to see who recovered in the replay, but I don't see why you shouldn't be able to use what the refs ruled on the field as far as the recovery goes. Go read the comments from the players after the game, several of them stated that the refs on the field stated the ball was recovered by Miami. And even if the refs wouldn't have said that Miami recovered on the field, from the replay you can see that Miami came out of the pile with the football. There's OVERWHELMING evidence that they got the call wrong.
What this shows is that the refs made two bad calls. First they called a td, then they blew the whistle ending the possibility to establish possesion of the ball.
The crew could not have screwed the pooch anymore if they tried.