My SO works seasonally in Venice, Italy where there are of course a lot of seagulls.
The birds go as far as land on people's heads and steal whatever food the person was holding.
Garbage bags are also considered a food spurce, so anyone taking out the trash so also at risk.
The only time I've ever been shat on by a seagull was when I was carrying a garbage bag.
Source? I’m really curious as to how shitting on people provided any evolutionary advantage.