"He is Mar" is an "Easter Egg" for the viewers, not a clue for Patrick Jane.

I noticed awhile back that there was no middle line to make the 'H" in "He," so the first part actually reads 'IIe'.  I never bought in too much that a dying person would bother to write "who is" so I figured it must be an address (ie. Apartment 2e, 15 Martin St.), or a Bible verse (ie. 2nd chapter Mark, verse 15), or a reference to a file number, work of William Blake or a date (ie. 15th of March/Ides of March).

But...

After the McAllister reveal, I had a hunch and went back and looked at his episode.  It is episode 2 (Roman numeral II), so that explains the IIe (2 episode).  But what about the rest, it isn't "is mar(s), is Mashburn, is many, or any of the others." It should be read 15 Mar(k), as in 15 second mark (using Mar instead of Sec or even spelling out Mark because it would have been too easily solvable, it makes sense to be cryptic with an Easter egg, not if you are a dying character giving an honest hint).

Exactly 15 seconds (not roughly, but exactly 15 seconds) after the title sequence fades out the camera pans and McAllister's face enters the shot.

http://imageshack.com/i/09bv6lj (Title sequence fades out at :13)

http://imageshack.com/i/j6zky2j (McAllister comes into view at :28)

That would support Heller's prior statements saying he knew who Red John was from day one, possibly he backed off of that so newer characters seemed more plausible to be considered for Red John?