Mahsa
I go through the same thing on a daily basis (except I have not been asked out). I think once one of us gets to a point where we are passing, it is hard to tell when we are clocked. It is a bit tough because a woman can be looking at you just to check how you are dressed like, and a guy can be just checking you out.
Usually when someone does a strange face, like with a frown or jaw hits floor thing, I know I have been clocked. This has only happened to me in my first week of full time. Otherwise, I don't think it is possible to tell. The best example I can give, is once when I was washing hands at the hospital, I remember you read that post and know what happened. Another time, when I was at a nightclub, I had a guy looking at me while I was asking for a drink at the bar, I thought I was clocked but he went on to start small talk with me.
So, getting stares doesn't means you are clocked. I think we have this impression because women are checked out more often than guys are and for more reasons. A guy will hardly ever look at another one to check his clothes out, as a example.
But! Once at lunch I saw two gay guys, one looked at me and went to say something to the one next to him who then looked at me with a smile. That IMO is clocked. I think gay men clock me easily

So, in conclusion, I think only the judgemental face is a giveaway of "you are clocked" or being called a sir. In any other situation, we are just overanalyzing.