I Rock

Last Saturday night I returned home around 1:30am.  Upon rounding the corner to my condo, I stopped dead in my tracks.  I looked at my company, back to the scene before me, back to my company.
"Was that there when you got here?"

Nope.

Spread out along the balcony in a perfectly straight line, were rocks.  Was this a sign?  How did rocks get along the balcony?  Are aliens trying to visit and communicate with me?  I have some mischievous friends (to whom I have given keys) to say the least and my mind went straight to them.

"You have to come in and make sure my condo is okay."

We enter. 

Nothing.

"Huh.  And here I thought my friends were trying to tell me I rock."

Sunday afternoon when I arrived home from church, there were the rocks.  Only changed in formation.

Weird.  Aliens?