wis-cacher, your question is a volatile one. Because the minute anyone comes on to say something like "the worst you'll get is a scram", is the minute someone else will conclude that any-such-talk is PROMOTING lawlessness, steering newbies the wrong way, etc...
So let me be careful in answering your question to preface it by saying that any such answer is not justifying, or "making it right", etc...
I too have often wondered when I see all-such-fears of : confiscations, jail, fines, tickets, etc... Put out as imminent fears we should all be leery of (and thus inquire and ask about every place we come to). I too sometimes wonder just how often this has ever really happened. I have suspected that if ever examples of those things could be shown, it would be for someone who a) was night-sneaking an obvious historic monument, or b) someone who couldn't take a warning, being obnoxious, etc....
I know of 2 friends who got tickets. One was at a historic federal park, and the other @ a CA state historic park, (not just a "regular" state park), where my friend wasn't aware he was on state park land. He was coming back from having hunted a private field with permission (he was using a trail to cross a vacant lot, and didn't realize it was part of the adjacent state park). In EACH case, it was only a ticket. And in each case, it was something silly on the order of a $150 hand slap.
My friend in the state park case was going to fight his ticket, because he hadn't been detecting, and had only been walking back to his car from an allowed place. However, when he saw the pittly amount on the ticket that came in the mail, it wasn't worth his time to take off work and show up to fight it. So he just paid.
Same for the other friend who got the ticket on federal historic park spot (which admittedly he should have known better).
I'm sure someone can come on citing worse consequences (the "jail" and "confiscation" part of your question), for seemingly innocuous places. All I can say to those examples, is that it's probably not unusual to find extremes of anything. I mean: so too can I probably find an example of a motorist pulled over, roughed up, car confiscated, jailed, ticketed, etc.... for nothing but a tail-light out. In other words: Examples of over-zealous cops can probably be found for just about anything in life. But that doesn't stop any of us from driving. You just be careful, use common sense, etc.. And you tend to see such stories as "flukes", not "norms".