Considering rabbits usually come out at night, it's rare to catch a rabbit in the act of invading your garden. There are a few ways to know whether your garden has been overrun by rabbits:
Keep in mind that rabbits graze close to the ground, so if your top-tier trellised tomatoes have gone missing, it's safe to say that a larger animal, like a cat or deer, have taken a liking to your veggies.
As far as rabbits go, they are pretty hard to get rid of, but not impossible. Here are some possible solutions for keeping rabbits out of your vegetable garden:
Build a Fence
Keep rabbits out of your veggies by surrounding the garden with chicken wire about 18 inches tall and buried in the ground by about 6 inches. If you already have a fence, perhaps you could attach the chicken wire to it with staples.
Use Garden Fabric
If there are specific plants in your garden that you don't want rabbits munching on, cover plants with garden fabric for a more targeted coverage.
Grow Scented Plants
Believe it or not, rabbits stay away from strong scents. Plant a scented herb plant like basil, oregano, or lavender around your vegetables to steer rabbits away. Rabbits also hate the smell of onions and garlic, so try planting batches of those plants around the garden. You also get fresh herbs and onions as a result, so it's a bonus for you!
Reduce Rabbit Habitats
To lower the number of rabbits in your yard in general, make your yard a less habitable place for rabbits. Fill in abandoned burrows and keep your yard as free as possible of twigs and leaves, so rabbits are less likely to nest. Rabbits also love burrowing in large shrubs and heaps of weeds, so keep those factors at bay.