My last deep dive into trespassing law was in Texas, but I think it's generally the same everywhere with some nuance. Criminal trespassing generally occurs when someone is told the leave and does not or comes back or disregards a No Tresspass warning such as purple paint or a sign. Sometimes breaching a barrier like a fence or gate can constitute Criminal trespassing. The problem is proving any of those things happened. Obviously if you have the party's name and address you can send them a letter certified mail. You can also keep a couple of letters on ya and hand deliver them to any future trespassers. Security guards usually keep warning cards on them as a means to hand deliver notice as they kick people off a property. If they return your sworn statement that you delivered a notice should by enough for prosecution. Beyond that they'd have to admit they disregarded the notice or the officer would just have to believe it was probable they saw it and disregarded the warning signs or paint.

Ultimately contact your sheriff dept and ask what the requirements would be for them to file a case
They should be able to tell you exactly what they want to have before they pick up a case.