As a quarry species, deer are programmed to identify friend or foe and will react accordingly.
They assess body language and clothing and so can tell instantly whether you are stalking and therefore a predator, or whether you are building a high seat, trimming rides, cutting logs or just sitting having a sandwich and a cup of tea, when you become an object of curiosity and they are quite likely to come and watch.
When they recognise your scent they will run but if they have seen you first and you are not too close, they will often check your body language before deciding whether to run.
They can recognise you by your face, as we humans do, and also by your clothing.
The best illustration of this happened to me some years ago. I was feeding deer in the park and they were gathered round for corn and carrots.
I was dressed as normal apart from the fact that my hat was in the car, against which I was leaning as I watched them feed.
A rain squall arrived and I reached into the car for my deer stalking hat and by the time I had clapped it on my head, the nearest deer were 150 yards away.