Alright...now that you guys have my head a-spinning lets set up some scenarios:
1) I am walking down the street OC'ing minding my own business when a LEO pulls up to me and initiates a "conversation." I can legally do what?
Do anything you want. Talk to him, walk away, dance a soft-shoe, quote Shakespeare, or run around in circles flapping your arms and quacking like a duck if you like....so long as you are harming no one.
2) I am a passenger in a vehicle OCing when a LEO stops my friend for some sort of suspected moving violation. I am obligated to do what and legally I DONT have to do what?
Nothing and nothing. There is no requirement to notify in Washington. (caveat: If your sidearm is loaded and the officer notices you are carrying, you ARE legally obligated to produce your CPL upon demand)
3) I am walking in a city park (Yelm) that conspicuously states "No Firearms Allowed" while Ocing when a LEO stops me and says "Don't you see what the sign says? No firearms are allowed in the park!" I say and do what?
That's up to the individual to decide. I can no more give you accurate advice on that situation than I could if some hairy 350 lb. guy in a hot pink tu-tu and fairy wings ran up and tried to kiss you on the lips. Everybody has their own personal comfort level when it comes to confrontations (and make no mistake...the officer HAS just 'confronted' you).
First thing I would do is start my recorder (if it's not already running).
You have the (1st amendment)RIGHT to tell the officer to 'piss off' if you so choose since you are doing nothing illegal. It probably wouldn't be the best course of action though if you simply want to go about your personal affairs unmolested.
or
You could cite chapter and verse of the RCW's which state that the sign is invalid and unenforceable, then point out that if he chooses to proceed with enforcement that he himself would be committing a criminal act (or multiple criminal acts depending on what action
or
You could engage him in polite conversation and choose your course of action from there.
or
You could just ignore him.
or
Any combination of the above.