Yeh drones are prohibited in all national parks I think. You have to apply for permission. I got fined in the Similan Islands for it - only 1000b though, was worth it for the footage.
Some places do have signs, some don't, you just get ambushed by some park officers ready with a pen and paper to write you a fine lol
Yeah i heard about this. stricter in the 'touristy' places but legally speaking I am not sure if park rangers are at liberty to do 'on the spot' fines (maybe im wrong)- but this is Thailand and sometimes a 'tip' can help both!
Yeh I'm not too sure. I'm sure people higher up are in on it too. Usually they just tell you to stop flying.