You might think that dressing like the locals and speaking the native language is enough to help you blend in when you visit a destination for the first time.
But, according those in-the-know, standing on the wrong side of the escalator, looking up and asking why "it's so hot" can all mark you out as a tourist.
And even something as inconspicuous as carrying an umbrella could make you stand out from the crowd in cities like Portland, Oregon.
In a thread on Reddit, users have been sharing how they spot the tourists in their city without naming the destinations.
There were some obvious responses, like the people going to tourist attractions, taking photographs of everything or wearing matching outfits.
But even if you're not intentionally behaving like a tourist, there might still be things that give you away.
For example, you could be mispronouncing names of the destinations or calling a building by its official name instead of its nickname.
Others pointed out that tourists tend to be more curious and can be spotted looking up to see the skyline.
Fredfredbug4 wrote: "Everyone looking up and blocking foot traffic."
Indeed, tourists getting in the way is a big issue and several people complained that visitors tend to be very slow whether it's on the road or on the pedestrian walkways.
And some are chided over standing on the wrong side of the escalators on the Underground.
Tourists also don't tend to dress for the weather, for example, by wearing shorts in December or a jumper in the summer.
In some cases, they're constantly complaining that it's the wrong temperature.
And then there are the unexpected reactions.
Paisatron posted: "When they joyfully run down a hot beach and shriek in surprise the instant they touch the water. It never gets old."
But some of the more unusual responses got other users guessing the city.
According to machobeef, carrying an umbrella is a sure way for the locals to identify you as a tourist.
While bingandworm guessed that it was Seattle, where the locals walked around in wet weather "as if it wasn't raining" and Samuel24601 tried London, machobeef revealed the correct answer was in fact Portland, Oregon.