Frequently chams do their business in the leaves and parts or all of it get stuck to a leaf. I wouldn't stress, just keep your eyes open for the brown part. Maybe next time you will get to see the poo.
(Thanks Chad ) Might as well start off the year with fresh poo pictures:
Sometimes chameleons will get their poop and urate dumping out of sync without it being a problem. Keep an eye out for the poop. If hydration, food, temps etc. are not within normal operating parameters, poop stoppage (impaction/constipation) can occur.