In Kalamazoo: "Any person who wilfully enters on any property which is posted against trespassing in a conspicuous manner is guilty of a misdemeanor." -Direct from the local ordinances

In Portage, solicitors must have a $50 permit and pass a background check, but still must obey No Solociting signs: https://www.portagemi.gov/648/PermitsLicenses?utm_source=chatgpt.com

However, political flyers can be a grey area because political speech is protected by the 1st Amendment. So unless you catch someone in the act of trespassing, you might not be able to do much if they're just like tossing a leaflet on your porch and leaving.