While there is no guarantee he will make the final roster in 2016, the signing of quarterback Ryan Mallett to a two year deal indicates something- and some Ravens fans will not be very happy about it (I'm looking at you, Sharp21 and others). After a down year ridden with key injuries, close losses, and ref miscue's, there is a school of thought that the team is not close enough to compete in 2016.
However, the signing of Ryan Mallett for 2016 indicates that there will be no down year, no rebuild. This front office expects to add a few players, let go of a few more, have the injured players return, and march right back to the playoffs. The signing of Mallett for 2016 was a savvy move, but also one that says "we expect to contend, so we better have a good backup quarterback." It is similar to the Matt Schaub signing in both cost and reasoning.
Mallett is expected to make it on the field this season, although he probably needs a week or so to pick up the playbook. I would expect a start or 2 from him in the coming weeks, and we will get a feel for him over the course of those starts and training camp in 2016. If he doesn't look good, the team can likely let him go for a minimal cost, but if he does, he would serve as Joe's backup in 2016 and even make a few starts at the beginning of the season if Joe's rehabilitation runs long. He will get plenty of camp reps, and that should be a great showcase for him since he probably will be looking for a starting job following the season. Joe's injury may even be one of the reasons he chose to come to Baltimore.
If the Ravens had thought they would not be a playoff contender in 2016, they likely would have drafted the next Tyrod or the next Troy Smith. But they didn't, and although they still could, they never have carried 3 quarterbacks since Flacco's rookie season, so I doubt they start now.
So there you have it: the Ravens signing of Mallett for next season tells you the teams thoughts. You don't have to agree, you don't have to like it, but it is clearly the Ravens intention!