Is it possible? Sure. But it's as likely to have happened long before humans showed up on the planet than not... and given the relative rarity of evidence for things that happened a long time ago, there's no reason to think we'd necessarily find the evidence or be able to definitively associate it with aliens.
The real question is... why would an alien civilization bother with visiting us? It's a mindbogglingly expensive proposition, and any civilization capable of getting here could get any sort of resource available on Earth in much vaster and easier to access quantities pretty much anywhere. Here's a cool image showing that Europa (one of Jupiter's moons) has more water than Earth does, for instance.