Hey allmIne, I don't ask permission because I want to keep the shots candid...
I use a 35mm prime so sometimes they notice after I take the shot, I just smile and go on my way. I suggest not be too sneaky, sometimes you go up to people and take photos of them and they don't even notice or care. If you act too sneaky though, people just become suspicious. Hope that helps. Thanks for looking at my photos and I hope to see some street shots from you soon