I've read that wearing athletic shoes "trainers" is a dead giveaway. I wear them anyway- my husband and I walk a lot and that's what's comfortable. Years a go I found a kid in a group of schoolchildren in Ghent surverying my shoes, and he asked me where I was from!

Like the previous poster, we carry cameras, maps and all the toursit accoutrements so we tend to stick out- but we're also low-key and I try to speak the loacal language, so we usually get a pretty good reception.