I know from personal experience that if you go around Disneyworld wearing white shorts and a brightly colored striped top (two different colors on two separate days) with matching socks, people will assume you work there. Princess costume not necessary.
There are people in as yet undiscovered areas of South America that would, at one glance, know that I can fix their computer. Even though they have no idea what a computer is, they would still know this.
I was walking back from a supermarket in Arbroath, Scotland (another business trip – I’d picked up, among other things, UK Cadbury dark chocolate for Pepper Mill) to my hotel when a car stopped next to me and someone with a London accent asked me directions. I laughed hysterically and said “I’m from New Jersey!”
Sometimes it’s intentional.
(An Improv Everywhere stunt.)
HA! Happens to me ALL THE TIME!
I was going to start a thread for the opposite of this one (“No, but I slept at a Holiday Inn last night!”) but this is a better place to tack it on.
I was at Home Depot in early December, trying to find a 1/4" x 8" #2 Phillips bit for a special project. Since it was just after Thanksgiving, the store was packed with zillions of people and the people in orange vests couldn’t walk more than two steps before someone asked for directions to something in an aisle far, far away…
A woman stood next to me and started gazing at all the packages on the pegboard hooks. She looked completely overwhelmed. She would occasionally turn and look around, fail to see anyone in an orange workshop apron, look dejected, and return to staring glassy-eyed at the wall of accessories. I had found what I needed so, after her third or fourth unsuccessful search for an employee-type, I asked, “Is there something I can help you with?”
“Umm–” the woman looked at me, failed to see a bright orange workshop apron, and asked, “Do…do you work here?”
“Well, no.” I shrugged, “But I’m pretty handy in the shop and you’re looking around like you have questions.”
Apparently I had broken the unspoken rule of Don’t talk to women in the tool corral lest you appear to be hitting on them or start sounding condescending because the four guys around me looked up from their accessory inspections and frowned at me and my breach of The Code. I only hoped my karma would come back to me when I went to a Williams Sonoma in search of a left-handed ice-cream scoop.
“Oh.” she looked dejected again.
“And, besides,” I tried to assure her I wasn’t hitting on her and waved to the four men glaring at me, “if you come up with something I can’t answer, I’m sure one of these guys is knowledgeable enough.”
Suddenly everyone around us was super-intently inspecting the label on a nearby accessory.
“Oh,” she looked comforted and explained, “Well…my son bought my husband a new cordless power drill and I was wondering what would make a good stocking-stuffer.”
“Well,” I responded without missing a beat, “It really depends how big his stockings are.”
“What?”
“Never mind.” I smiled and glanced at the accessory rack. She had been gazing glassy-eyed at the shrink-wrapped replacement drill bits, but I reached a couple feet over and grabbed a plastic box filled with odds-and-ends, “Here, ya go: Twelve-piece bit set including a magnetic extension and a case. That’ll get him started and what he doesn’t have already he can find in giant kits or on-line as he needs them.”
“Wow! This will go so well with my son’s gift!” she was obviously truly grateful, “Thank you so much!”
“Oh, don’t thank me.” I shrugged as I walked away, “You still have to pay for it.”
–G!
To me as well. I have been asked for directions in Rome, Istanbul and Athens by people speaking the local language. Heck, even in Tiananmen Square and the Forbidden City in Beijing, I was asked dozens of times to take others’ pictures.
I (well my wife initially tried to figure it out and believes that to be the reason) chalk it up to being a tall large non-scary guy. As similarly I get asked to take pictures for groups in front of every monument, in museums, etc. too. I lived in NYC for many many years so I know how to not look around or make eye contact so it is usually people just appearing by my side and asking without any visual cues.
OTOH, I can be behind the register with the light on, ringing up items and wearing my red shirt with the store’s logo on it, and someone will come up and say “Are you open?”
Looking annoyed, someone actually asked me that, once. I replied, “Well, yeah, that’s why I asked you in the first place.”
If others who work in your store are inconsistent about making sure to turn those lights on and off at the appropriate times, or have ever been acting as you describe and then told someone “Sorry, this checkout is closed”, then I can’t blame them for not being sure.
Otherwise, I CAN blame them. 
Take it from one who knows, turning your light off makes no difference to some people. They will come up and start putting their items on the counter. “I’m sorry, I’m closed. My light is off.” “Oh, I didn’t notice.”
I’ve had people put their items on the counter when I was counting out my money. Really!
The best way to avoid this is to wear black tee shirts with skulls/flames/pentagrams/weapons and a scary sounding/totally illegible band name on it. Unrelated, but there are a surprising number of metal heads working at the Trader Joe’s near me.
Always learn the local phrase for “I don’t speak [local language].”