In my opinion, the single most important event of season six this far is Partridge saying Tyger, Tyger. The fact that he chose to say those two words instead of a vast number of seemingly more helpful word combinations is important. It tells us that either
1. He is Red John (and thus still alive)
2. He works for Red John and has been given a message to relay
3. He is such a fan of Red John that he does not want to reveal his identity
4. He simply does not have a better way to describe Red John's identity.

Out of all of these 2 and 3 seem the least likely. Red John does have many followers, but they are usually strategically recruited. I am not sure what value Brett Partridge gives Red John. Also, even if Brett Partridge is a super fan of Red John (we know he knows a lot about him, and gets excited to see his killings) I think he would still be upset enough to tell Lisbon his name. This also assumes that Partridge was able to find out on his own that Red John had recited the Tyger, Tyger poem to Jane, another stretch of the imagination.

While number 1 is certainly possible, it does not leave much to debate, except when Partridge will re-enter the show. The fourth possibility is the most intriguing as it confirms the "He is Mar" clue from a previous season. In both of these cases it would appear the Red John's identity was not easily expressible. If we assume that Red John did not write the "He is mar" message, and for the sake of this theory assume that Brett Partridge is not Red John, then we just have to find a connection between the two messages.

First lets go back and look at some popular theories for "He is Mar"
1. He is many
2. He is Married
3. An address: 15 mar
4. He is Mad

Now someone find a connection between this and the Tyger Tyger poem, because I am stumped.