Bmacd88, welcome to the forum, and thanx for your reply here. And thankyou for your service to the public, doing a stressful job like that ! Interesting to hear from someone with LEO experience, as an fellow hobbyist.
.... If there are no signs, there is no need to ask first. Why get a "no" answer right away when if you went without asking, maybe nobody cares. If someone does care, they tell you "please leave" and then you just leave.....
That's my bee in-my-bonnet contention

And now we're hearing it straight from someone who's "been on the other side"
However, the usual come-back line from the skittish crowd will be this: "It gives a black eye to the hobby", and "could lead to rules being written". I disagree, d/t the following:
a) Conversely, someone asking where it wasn't necessary to ask (and/or no one would have noticed or cared), could EQUALLY (or more-so in my opinion), "lead to rules". It just puts a sort of image to the person fielding your question of something amiss or wrong or harmful, such that you needed to ask (lest why else would you be asking, if the activity were innocuous and harmless?). Thus the very act of asking, can caste aspursions on your activity. Thus simply lending itself, to the "easy" and "safe" answer.
b) So guess what happens the next time that pencil pushers sees another md'r out there? He recalls the earlier inquiry, and thinks "aha! There's one of *them* ". And starts booting others.
c) Lastly, it's sort of circular logic anyhow. Because if someone was "booted", how can that lead to a "rule" ? Because, gee, if they "just got booted", then logically, there must've been some "rule" that was invoked, to have booted them in the first place ?? So how can any added layers of "rules" change that ? Therefore the "black eye" and "leading to rules" notion doesn't hold much weight.
.... If by chance they call the police first, all the officers are gonna do is ask you to leave. Nobody is gonna have their gear confiscated or get arrested....
Another of my contentions ! And again, hearing from the other side of the equation ! Anytime the discussion of "can or can't you detect a certain place" comes up, the sobering caution of "tickets", "jail" and "confiscations" can come up. I've seen this many times. But then at a certain point, you have to ask yourself and them: "Is there any actual examples of this ?" And then you hear the sounds of chirping crickets. And if any examples CAN be shown, they are invariably for someone night sneaking an obvious historic monument, or someone who can't take a warning, or somehow being obnoxious, etc...
..... By law, the only way the officer can arrest you is if there is a posted "no trespassing" sign.....
Just to be clear, in California, a fence also qualifies as constituting as a "sign" as well.