Hey silver surfer: odd that this follows right on the heels of your episode (which turned out to be successful). I would bet though, that even though you got your "scram" turned to a "go ahead", (once the silly issue of holes was worked out) that if you'd subsequently told the fellow "
Oh goodie! does this mean I can take objects out of the city's park, for display on my own mantle place? 
" that they might have reconsidered their decision on yet OTHER grounds.
Sorry to say, that this "collecting" vebage is actually there, in almost any and all parks and public land. The logic is simple: What's to stop someone from mining for coal, setting up harvesting of some natural resource, or other such admitted abuses? (ie.: if everyone picked up a pretty rock on the beach, guess what would happen if a million people did the same thing?). I mean, for example: there are some campgrounds that prohibit picking up firewood off the ground (ie.: can't pick sticks, pine needles, etc... to use as kindling). You might ask "why not?? that's stupid?" But
before they had this rule in Yosemite's more well-used campgrounds, entire acres of land around the more developed sites were continually being stripped of all ground cover! Even to the point where people were sawing down lower hanging branches! So you can see that .... in order to be uniform and accross-the-board, they do, in fact, have these "no collecting rules" most anywhere, if you were to look deep enough and hard enough
But JUST LIKE IN METAL DETECTING, we ALL know that if your little daughter picks up a pretty stone for her grade school art project, does anyone
REALLY care? Of course not! *But* is she technically breaking some law? I suppose. Will anything become of it? Probably not, unless she or you go "ask permission".
I apply this same psychology to md'ing: If any of us looked long enough and hard enough, into ANY public land's rules, we'd probably ALL find numerous fronts to disqualify ourselves from ever stepping off the sidewalk. But does that mean anyone really cares? Probably not.
If someone does come up with to take issue with us, as in kawalbear's situation, then you can try to fight it, I suppose, or just avoid that one park or one gardener, in the future. I have even gotten to where I do most of my hunting at off-hours (late Sunday afternoon, after 5pm on weekdays, or actually, even night-hunting) JUST to avoid busy-bodies, to begin with.