Whether you can see it or not, you have bird poop (and bird urine and insect excrement as well) on EVERYTHING outside. That's why it's ALWAYS smart to rinse off your veggies. Oh, it's also on all your soil, which is one good reason to wash hands after digging.

If we tossed our veggies for fear of bird poop, we wouldn't be eating anything from the garden.

Interestingly, most bird poop is green, such that you won't easily recognize it on lettuce. The white stuff is actually the urates and comes from the kidneys, along with a liquid portion. When we digest proteins, it comes out as soluble urea, which is pretty clear. When birds do, it comes out as uric acid, which is insoluble, and a white paste. The white stuff is probably the cleanest stuff that comes out of a bird.

Wash them with clean water. It comes right off. If you like you can rinse them outside and again in the kitchen sink. You don't have to use soap or chemicals, water works great. But if it really freaks you out you can purchase or make produce wash. If it really really freaks you out and you just can't wash them, you can pitch them. But do keep in mind most if not all the produce you consume is grown outside and they just wash it too to get debris like bird poop off, and they don't sanitize it.