The same way we pinpoint where light or sound is coming from. As you get closer to the source the signal becomes stronger and more pronounced and you know. We dont really think about it as we do it its just ingrained in us. We process light and sound faster then we usually do scent but we do process it.
Also something we talk about in here is congruence or not acting in opposition of your mone signature. Because your natural mones come from your own emotions, behaviors and identity you never have to think about that because you cant help but be congruent. With synthetic mones there is some effort though.
If you wear something like IO which sends a friendly open signal you have to get out there and mingle and be friendly and open when people respond to you pheromonally. If not you just confuse people and they have a hard time processing where its coming from.
This has been discussed a few times, maybe this post will help.
Tisha