If it's fly or insect poop, you can try the Bounce dryer sheet method (see video below).
However, if they are in fact what lovlabs is describing, --shotgun or artillery fungus-- they will be much more difficult to remove (without leaving a small brown spot). You can try this solution and a lot of elbow grease:
1/2 cup of dishwashing liquid
2/3 cup of trisodium phosphate (TSP, Soilax, etc.)
5 cups of 5% sodium hypochlorite (household bleach)
12 cups (3 quarts) of water
Put this solution in a spray bottle and apply to area. Let sit for about three minutes. Take a damp microfiber cloth and rub until spots are completely gone. Apply more solution if necessary while rubbing. I suppose you could even rub with dryer sheets too for that matter.
There are alternate formulas out there too so I'm sure others will chime in with their suggestions.
If bug poop, here's one method using dryer sheets:
Easy Way to Clean & Remove Dead Bugs From Your Car - YouTube