I used to run a fleet of 123 Mercs, it actually recommended in the handbook to put newspaper over bird sh*t, soak it and leave it awhile and it would come off without marking the paint. It worked!
Paper towel wasnt invented then IIRC and paint wasn’t water based but I still use that method cos we have thousands of seagulls around here, a total PITA and they sh*t for Britain. Rolled up newspaper and cold tea is especially good for cleaning glass even though we now have proprietary glass cleaners. Dead flies hate hot water even more...

1969 4/4
1995 plus 8
2002 Aero S1
2013 M3W
2014 Plus 8