One thing I'm trying to figure out is how to tell for certain whether employees in stores have clocked me or are just doing what they would do to any customer. When someone comes to ask me if I'm finding everything I'm looking for, I often have a moment of panic unless I know this is standard for the store. In some places, after all, the attendants will leave everyone alone, and in others, they will go up to many people to ask them if they need help. But I'm convinced that some employees, uncertain if something is "off" about someone they've seen, will approach them to confirm or disprove their suspicions.
This happened to me recently in a Kohl's. The few times I've braved going there en femme, I generally have no obvious issues, and the cashiers are fine, even once my voice and male name on my card have given me away for sure. But one time, an employee was looking at me as I browsed, and after a minute she came up to me and asked if I was finding everything all right. Normally, no employee asks me anything in Kohl's. I said "mm hmm" in as neutral a voice as I could get, but I'm sure my voice still gave me away. Later, she followed me into the dressing room area and knocked on my door for no clear reason after walking past a number of presumably empty rooms. I told her I was in there, and she said "oh!" and walked way. Maybe it was in my head, but I just got a weird vibe from it.
This may be going against the grain, but I sometimes think that--depending on one's passability overall--wearing bolder makeup (not drag makeup, but a noticeable lip colour and/or eyeshadow) can help you pass rather than barely noticeable makeup, since--at best--that makeup can help gender you at a glance. When I was just wearing jeans and a t-shirt and subtle makeup, I got more stares; when I began wearing red lipstick and/or some shade of eyeshadow that was not in-your-face-but-was-noticeable, people didn't stare as much.