I won’t insist on those particular examples.
Easier to differentiate typewritten, but if I was sloppy in my writing, does this 一 二 十 mean minus equals plus (of course a nonsense equation), minus equals cross or one, two, ten in Chinese or Japanese.
Edit: The little uptick in one and two aren’t there in written Chinese and Japanese, with the possible exception of calligraphy.
Thinking about it, Arabic numbers MAY be the most universal symbol (in the sense that they represent something abstract), as it’s often intermixed with native language text, particularly in markets.
The Italian symbol for range looks like the American symbol for division (dash with a dot and above). Rather confusing.
Even though the stop sign might not be always used for stop, it is a ISO/ANSI standard for Danger. The yellow triangle with an exclamation mark means warning.
And there’s the yellow triangle with the jagged arrow which means high voltage. There might be places that don’t use it, but it is quite universal.
If ANSI and ISO agree, those are the symbols which are practically universal. Of course, they don’t always agree, and there are local variants.
A sign including a wheelchair typically indicates accessible areas.
And did you know there’s the Globally Harmonized System of Classification and Labelling of Chemicals? I first learned about it a few years ago. Switzerland has, for many years, used their own signage. Recently they decided to join the rest of Europe. No rushing such things, of course.
Does ° (degree symbol) get around much?
Yes, I know 一 isn’t written in the middle like minus and the top stroke of 二 is shorter than the bottom stroke, but I said I was sloppy in my writing! 
There are the copyright symbols © ® ™
Only the first one is a copyright symbol. The other two are trademark symbols.
The Chinese knock-off manufacturers don’t recognize or acknowledge any of them! :rolleyes:
It’s hard to imagine anyone making a worse case for something being universal.
Pi is used all over math for other things than the familiar constant. Most notably for homotopy groups, where it is absolutely standard. I will grant you that union and intersection signs have no other usage–at least none I am familiar with, but they will not be widely know outside of mathematics.
I want to note that this thread is about graphic symbols, not hand gestures. Or at least I meant it to be about them, although I failed to mention that in the OP. Also lets ignore issues like whether the symbol can be easily confused with another symbol under poor viewing conditions. Assume people get a clear view of the symbol. (Some day I’ll anticipate all these kinds of things before I write a question.)
Suggstions that look likely: copyright and trademark symbols (© ® ™), degree °, and maybe pi (π). I don’t think the biohazard symbol qualifies nor do any other mathematical symbols. Even the obelus (÷) is probably not universally recognized, although it may appear on some keyboards (it doesn’t on mine, though).
And perhaps I was wrong about all the currency symbols, at least the yen. The centavo symbol is certainly not universal. The dollar, pound, and euro signs I’m going to stick with though, even if they can be mistaken for letters.
The exclaimation in a triangle is a big maybe. I know it’s a road sign in some places (although it’d cause confusion around here if seen on the highway) and I’ve seen it in instructions, but I’m not sure it’s that universal.
Yes, to the extent that there are degrees of “universal” (and I’m sure there are people who will think that that word should be an absolute), those are certainly the most widely recognized. Even illiterates will often recognize those.
True, but is it relevant? If the same symbol has more than one meaning, I don’t think that disqualifies it from being “universal” in the way the OP is asking about. At least not if at least one of those meanings is known by everyone who recognizes the symbol.
I wouldn’t include road signs because there are some variations across countries.
How about the no smoking sign?
The Star of David? I guess some people wouldn’t recognise it. (I’m assuming you’re talking about what adults would recognise, FWIW). The swastika isn’t universal because it has a different meaning in Hindusim, though then it’s clockwise rather than counter-clockwise, so maybe it counts.
Are they symbols? I assumed the OP meant stuff you see in writing, not gestures.
V for victory and v for get stuffed are different to each other - it’s pal out for victory, palm in for get stuffed.
The peace symbol, though, which started out as the CND logo, is probably very widely recognised, but I wouldn’t say universally.
Welcome to the world of people trying to safeguard stuff like nuclear waste that will be lethal for thousands of years.
How do you say “Stay the hell away from this!” without knowing what languages will exist?
My apologies and I’ll give you a right-way-round Winston V.
I disagree that the pound, euro and dollar symbols are universal. If someone has doesn’t do monetary transactions in anything but their own currency, they may not recognize those. To infer that they’re not “relatively intelligent” is extremely dismissive and insulting. They’re just not exposed to international currency. I knew about the Euro, but when I first encountered it on the internet, it [took] a good bit of thinking to associate the symbol with the word.
That said, arguably not a symbol, but the man and woman images on Voyager 1* is *universally recognizable by any human and possibly even some highly intelligent animals or alien being who may know about Earth.
I agree for most of them. But see discussion above for the stop sign.
Possibly.
Not sure that would be recognized everywhere. But as someone pointed out, the Christian cross is one.
I did say educated people, so yes, that pretty much means adults.
Is the swastika still in use in India to mean something other than Naziism? Or did the Nazis ruin it for them too?
In a later post, I made the point that I meant graphic symbols, not hand gestures. So let’s skip the side thread about the peace/victory sign.
SIGH For those seeing Nazi swastikas everywhere in Hinduism and Buddhism, they’re not Nazi swastikas! Non-Nazi swastikas can be right or left facing. But they’re almost never at a 45 degree cant like the Nazi version! https://en.wikipedia.org/wiki/Swastika
No need for the snark - we’re talking about what people actually recognise, not what they should recognise.