I've hunted lots of court-house lawns. But there's a LOT of desk-bound bureaucrats in such buildings (go figure ... the very NATURE of such a building). So unlike regular parks, schools, beaches, etc.... this one is going to be one that is best hit at ... uh .... "off" times of day. Like later on a Sat. Afternoon. Or early on a Sunday AM. Or on a federal holiday, etc...
At the ones I've hit (and done well at several!) I have not "asked permission". If there is no law in that city (like in their park's dept's park's rules) that forbid detecting, then in my opinion, permission is not needed. But that's not to say that someone can't gripe. Heck, you can get a gripe for being at a park or sandbox. You can never 100% gaurantee "no busy-bodies", since we're in an odd hobby that has connotations and draws lookie-lous. So ... sometimes you have to pick times wisely, so as not to swat hornet's nests. You can certainly go ask if you want, but my suspicion is you'll probably be told "no" (the "safe" answer), when in fact, perhaps no one would ever have cared or noticed (unless you were being a nuisance at high noon acting like a bullseye for attention).
