I can't imagine a sign for what, but I'm glad that you captured him/her. I love when wildlife visits my yard, even if it's raccoons who love to tear up the lawn (well, my lawn is on its deathbed anyway, so not much damage here).
I can hardy wait for the cooler weather of fall. The baby possum is so cute, some people don't like them but I do, maybe because they love to eat snails. Racoons, that's another question ~ horrible!
A SIGN? Well, perhaps to *PLAY POSSUM*, quiet your mind, observe and keep life simple.