This is an area where I employ the old "Easier to ask for forgiveness than permission" law. Sounds like I might suffer for that in a few places, but generally if you ask you'll get a "No" and if you get caught you'll get a warning. YMMV if you like to climb trees across the street from the PD or City Hall.
I climbed a couple of Sequioas and never heard a peep from anyone about it. When I practice for TCC's I sometimes get questions from passersby but never cops.
Chased out of Eastwoods twice but have climbed there since with no issues.
Also chased out of the Cypress at Zilker on the lake. But I have climbed that one with no problems also. I just did it at 6 in the morning. Onion Creek at SE Metropolitan Park has a bunch of nice trees. Its a little bit of a hike with some brush whacking but that makes it all the more fun.
In Boise...yes, Boise=Tree...Idaho there is a law on the books that prohibits tree climbing unless you're going to retrieve an RC plane, kite or Frisbee. Seems like adding a ring to flip into the tree would make sense. Then climb to the top in order to get a good TIP
In Minneapolis two friends were politely asked to come out of the trees. If not, the ticket would have been for 'vegitation molestation'. Sounds more like a sex offense.
Keep a low profile and look professional...and follow Kieth's mantra...forgiveness not permission.