It's on the back of the chassis, I think. Look on the left side.
It should look like L-012345, or "L-" with a 6-digit number after.
I think the number is sequential, not a coded date-based thing.
If you find out what the scheme is, let me know. I haven't called Mesa or anything, but I've been unsuccessful in finding a DOP for mine... I'm only assuming mine was made in '06, but I could actually be wrong about that.
