Of course anyone could call the police claiming 'alarm' from you possessing a firearm in plain view, or possessing one at all... Usually when the police respond they will get both sides of the story and make their decisions based upon boths parties sides, and any witnesses (this is the department procedure where I live). You may want to contact your local PD to inquire about how they handle these situations.
Threatening is a vague term, basically it is supposed to be somewhat vague as by doing so it can be a blanket term and used for a number of different reasons.
Your firearm should never have a reason to leave your holster unless you need to defend yourself, or others (if statutes allow).
Threatening could be considered as walking around with a firearm with your hand on it, or holding it freely in your hand, brandishing, and anything else of the sort. Also, I have heard of account of people getting into arguements, and the other party was oblivious to the firearm on the other parties person, then when they become aware are 'alarmed' and get the police involved.
Some things I take into consideration when OC'ing are my dress and my actions. I have voiced several times that oc'ers in particular need to hold themselves to a higher regard when doing so as it 1) will help desensitize people to firearms 2) show people what a responsible firearms owner is.
By doing so, you can eliminate almost any reason the police would have to come down on you for OC.
As far as 'display' of the firearm, it should be legal to carry it however you like, just not in your hand, but obviously if you just stuff it in your pants with the butt showing, or if you carry it in a sling you will probably get more attention than if you carry it in a holster.
Just use common sense when going about it, if you oc enough you will probably have a police encounter as you are likely going to encounter a citizen who is 'alarmed' or falsely belives it is illegal to carry. This is where you need to be able to articulate the legality of your business to the police and voice your side to them. If you can do this you should be fine.
Good luck! -- I take it you have not OC'ed yet?