Every now and then a few leaves on my large indoor hibiscus get eaten a little bit in a very geometrical fashion. Only a few leaves and not often. So no danger to the plant, but I'm very curious. I've looked and looked for a critter.
i would take a flashlight at night after the room has been dark a few hours and see if you don't have some kind of worm eating them. not too likely since it is indoors but i can't think of anything else that would cause that kind of chewing damage without you seeing it.
I agree that it looks like catapillar/worm damage. Does your plant ever go outside for awhile? I can imagine several ways for a worm to get in the house, such as on another plant, cut flowers, potting soil, etc., or a stray moth laying eggs that hatched.