If it has etched into the clear, you may want to start out by using a mildly abrasive polish. Something like Meg's ColorX by hand, or if you have a PC, Cyclo, or rotary you could use something like Meg's professional line of polishes ,or one of the many "boutique" brnads of polishes - Poorboy's World is one of the most user friendly I have found. If that doesn't help, you may have to resort to wetsanding to remove the etching.
Quite possibly, it could be staining, in which case a chemical cleaner polish would help reduce the stain. You may also want to try a vinegar/water solution before you get too aggressive with it. Soak a microfiber towel and let it sit on the stain and it should help break it up/make it easier to remove.
You may also want to start keeping a microfiber towel and some sort of QD or waterless wash in the truck to remove bird droppings ASAP.
Keep in mind that waxes and sealants (no matter the brand - Zaino included) are a sacrificial barrier (and very thin), so something as potent as bird poo will do a number on them very quickly.
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