Originally meant small tokens or food left by an older (often rich) woman (cougar) for a much younger man to keep him coming back, in a positive way. The meaning has changed slightly to mean any personal belongings left by the cougar in a negative way.
Oh man, I almost got so busted last night.
Why man, what happened?
Oh, my girl found cougar droppings in my bedroom.
What?!? Did she leave her bra?
Hell no, she left her teeth in a glass of water. Lucky for me, I was able to tell my girl that my moms had visited me and used my room while I slept on the couch.
Baked goods or other small gifts given to or left by a cougar to a young buck. These "droppings" are meant to entice the prey to stay longer or make more frequent apperances.
Moe: "Man these are great cookies! Did you make them yourself?"
Larry: "Nope, they're cougar droppings from that chick I met at the wine bar."
Moe: "Dude these are so good, they taste like my Mom's cookies."