Is it just a movie cliche, or are they really out there? Where have you seen any? Do they overstate how far you’ll have to go before you’ll have the chance to fill up again (to improve sales), or do they tend to be accurate? What’s the longest distance you’ve seen mentioned on one?
I don’t recall every seeing a private ‘last gas’ sign, but I have seen official state-installed signs that said something along the lines of ‘Next gas x miles’. Only on the road between NoWA and SoCal I only remember one. More common are signs indicating the next rest area.
IN 1976 I went through the the southwest. There were many times where the next stop was over a 50 miles away, and even over a hundred. The next stop was often a gas station, restraunt, and two houses. The signs were up at that time. I don’t know if Kiwki Trips and such have proliferated enough to remedy that.
We have signs like that in Northern Quebec, except in French.
Driving through the Everglades in Florida from Fort Myers to Hollywood there is a sign that says last gas for 50 miles.
When I moved from southern CA to WA in 2004, I recall seeing signs along I-5 in central California reading “Next services 22 miles” and so forth.
They have them in Australia. There are patrol stations here that can be a tank’s worth from the next one. You even see them in the metropolitan areas (last cheap petrol before freeway).
Here’s a wonderful tale of karma related to this (supposedly true):
A city slicker stopped at a pub in the outback during a heatwave. The little settlement was the only inhabited place for hundreds of miles. This guy walks into the pub wearing a singlet, ignoring the dress regulations sign saying “no singlets” because he just thinks the locals are hicks. The woman behind the bar gestures to the sign, and politely asks him to put a shirt on. Our city boy gets uppity. The woman insists. The city boy tells her “you can stick your pub!” and storms out. Then he goes next door to the petrol station because he has to fill up - has to. He waits and waits. Finally who should come out of the little office but the same woman who was in the pub. She says, “After consulting with my husband, we have decided to stick our petrol as well.” They made him stay there several days. 
Seen them in Canada - 150km or so, IIRC.
They’re all over the interstate highway system, usually “next services xx miles” or, “last rest area for xx miles”.
Drive from LA to Vegas and you see them everywhere.
There is a sign like this inside of Everglades National Park between the entrance outside of Homestead and the end of the road at Flamingo. It has been a few years since I’ve seen it. I think it says no fuel or services for 30 miles.
The Pennsylvania Turnpike has a “Last gas” sign out by New Stanton (east of Pittsburgh). You can get off and get gas at any exit, but you can’t buy it on the Turnpike westbound from there until you get to Ohio.
What’s a “singlet”?
During a road trip several years ago, my sister and I passed a sign in southern Utah that read “next service 100 miles” or something very close to that. We had enough gas, but about halfway through, our car wouldn’t accelerate properly and was acting, in our expert estimation, wonky.
We actually made it to the next rest stop, in fabulous Beaver, UT, and our car died right in the middle of the off ramp. Luckily we were next to a service station and were able to get it towed. Something was wrong with the transmission, I don’t remember what, and we ended up staying there two days and paying a small fortune for repairs.
That was a fun trip.
[QUOTE=Sunspace]
What’s a “singlet”?[/QUOTI believe we would refer to it as a “wife-beater.”
We drove south along the California coast a few years ago, and somewhere along the way- I honestly don’t remember where it was- we approached a kind of ramshackle gas station on the right side of the street with gas that was about $.20 higher per gallon than we had seen that summer. Handmade sign out front advised it was the last gas for, oh I don’t know, maybe 50 miles. We sucked it up and filled it up.
About 5 miles down the road we passed a chain gas station, priced about $.20 less than we had just paid.
Grrrr ensued.
We even have those signs between San Francisco & San Jose.
Whereas ‘wife-beater’ in Britain often means Strongbow or Stella Artois. 
I’ve seen them on I 10 between Phoenix and Los Angeles. The desert isn’t a place to play chicken with the gas gauge.