Departing Mexico City airport to USA with permanent resident

Hello All, I always fly out of Ixtapa airport with my USA passport and Mexico Permanent Resident Card. I am required to go the immigration office at the Ixtapa airport before I board the plane and sign a ledger. So now I am departing from Mexico City airport....do I need to find the immigration office at the Mexico City airport and sign a ledger there? Thanks in advance for any info/ direction/ experience. Saludos.

I am also a Permanent Resident and am thoroughly confused about the issue. A couple of months ago I flew out of Mexico City to Colombia.
I happened to walk by the Immigration 'booth'.
I did have them 'stamp me out' without actually knowing if I was required to.
I could have asked the officer, but I had a sense that my level of Spanish would lead to confusion?