If you do not know about the M + L Egg on Sierra 117, then this what it is.
On a certain tree, a heart with M + L with a date in 1997 is carved onto the tree.
What do you think M + L Stands for?
I think:
Mario + Luigi
EDIT:
Turns out it was 1995 not 1997
[Edited on 08.24.2010 5:50 AM PDT]