I've never taken hallucinogens as such (shrooms, acid), only pills, but I definitely get visuals.
The most common is stuff around people's faces. I quite often see green grids on faces when I'm coming up. The sunglasses thing, of course. (BTW somebody posted to say that if you know somebody is seeing sunglasses on you, mimic taking them off to cause them to trip. I tried it and it really does work).
However, I also seem to see a lot of disfigured faces, as if people have had really bad skin transplants/burns. It sounds horrible but it actually feels as if I'm in some spoof Zombie style film and appeals to my black sense of humour.
The most embarrassing thing that happened was spotting a guy in a London club who I was convinced was a bloke I'd bought pills off at another club the previous week. I started chatting to him and he was very friendly (sympathetic is probably a better word). When he told me he was working in the second room I started doing all this wink-wink, nudge-nudge see-you-later stuff. He just walked off bemused and I turned round to see my girlfriend killing herself laughing at her twat of a boyfriend.
Still, I love the visuals and I do believe that they are more likely to happen the more pills you take in a session (unless it’s just the mixture!!).