I don't think it's illegal, but it's against the letter of hosts rules; I've taken SLR cameras into concerts. I know they don't want flashes going off or film auto-rewinders droning on, or cameras chirping. I've gotten some nice pictures. I generally do this at concerts where if I got kicked out it wouldn't be the end of the world. Having the camera in your wife's purse is an excellent way to get it in; jacket pockets can do also. Security staff is mostly looking for people bringing in booze I think.

I trespass sometimes, but that's not a big deal in my wooded area. "Posted" generally means no trespassing if you are hunting or trapping or have a dog that will crap on their land. Or at worst, it's posted so that people won't see and snitch on their pot growing skills, their malfunctioning sewage system, or the trees they cut that were too close to the water to be cut. We don't have industrial sites to trespass on really.

Someone hiking through with a camera looking for nature scenes isn't a problem and would probably get you a good conversation going if you have antique LF equipment, as most of the local land owners are fairly antique as well. If you have a kindle or library access, read thoreau's "walking"; that's sort of our situation regarding trespassing and our ambivalence to it.

As far as keeping a hardhat and vest to look like a surveyor, don't dress too nice! I showed up a worksite (with permission) one day to take some photos of ledge blasting. I had a nice 3-season jacket and dress pants and clean shiny hardhat and pelican case. I didn't get far from the car and worked stopped; the workers were certain I was someone important from the state checking up on them. The property owner straightened things out. On the other hand at work we're often hiking through the woods near homes with a surveyor tripod and a optical fusion splicer, and we're often mistaken for surveyors.

I've camped where I wasn't supposed to (in a state park that was closed for the winter). I've urinated outdoors as God intended us to, but man would deem indecent exposure.

I've taken photos breaking the rule of thirds, I've put horizons in the center of some photos, I've taken handheld photos at shutter speeds less than the reciprocal of the focal length (without VR/IS), and I have ignored the sunny/16 rule.

I'm not overcome by rebellion in breaking laws, but it's impossible to do lots of normal simple things without breaking some laws. I wouldn't attempt dangerous activity while trespassing (such as base jumping or causing plainly visible OSHA violations) and prefer a leave-no-trace style. I don't want my presence to cause actual risk or damage to landowners. If more people trespassed like that, there would be little need to post land.