Context matters a lot here.

Like others mentioned, localization and your primary userbase should inform you whether to use $, €, £ or ¥ as 'standard' symbol. It might also be possible to do a location-check (via GPS, or IP) and display whichever icon is most appropriate.

If you don't know your userbase's location or currency, you could choose to go with ¤, which is the official stand-in symbol for unspecified currency. However this relies on them being informed enough, and as such wouldn't be advisable on a site for regular Joes.

But beyond that, it depends on what you're depicting. If it's about invoking the idea of money, you could combine the $ with other elements, for instance placing it on a bag to indicate you're not talking about a specific value. But be wary of using just the $ on its own as it is likely to be misinterpreted as actually meaning 'US dollar' instead of the broader "money".

Alternatively you can go for a more pictorial approach and show some bills and some coins. Even if you use green bills that look like USD bills, not using the actual $ symbol could prevent anti-US people from having negative associations.

Surely the best symbol for currency that will be universally understood would be a note and coin as every currency uses both paper notes and coins most currencies use banknotes and coins.

Given this is a simple symbol for "currency", agnostic to culture, the great majority wouldn't have heard of cryptocurrencies, and may have once heard of Bitcoin so they wouldn't need to be represented to be understood by the vast majority.

Also, whilst many of use credit / debit cards for most transactions, we are still acutely aware that we can have cash, use it for transactions and no doubt still have some various notes and coins in a pockets / wallets at any given time.

Be sure to remove any currency symbol, and you're good to go.

Something like (without the Wikipedia text and people images):

Image source: https://commons.wikimedia.org/wiki/File:Money_Coin_Icon.svg

The '$' symbol may be recognised by everyone, but if you want to avoid any emotive patriotism, how about a gold coin?

Historically, this question has been debated for quite a long time.

There is a "Generic Currency Symbol," which looks like "¤" which has been used since at least 1985, where it was included in ISO 8859-1 (Latin-1). In theory, that is the symbol you want. However, I have never seen it used outside of reading about the code pages themselves, so that just goes to show the challenges we face with currency symbol.

Lots of people have given good reasons. I don't think you'll get many Russians growing too irate at the $ sign but it is an interesting thought.

Another possible problem with the $ sign is it could lead people to thinking costs are in dollars. Which dollars is this? It needs to be clearly said or else you could get a particularly ignorant Australian not realising that this site could possibly be using another sort of dollar and thinking he's found a real bargain.

A standard that I've seen around is to have a combination of currency signs. $¥€£ gives you a decent cross section of the global economy with some recognisable signs. This I think clearly says money in general without leading people down an avenue of getting stuck on thinking about one currency.

The answer is simply

of course, absolutely not

and it's surprising there is so much humming-and-hawing about it here.

It's an extremely US-centric idea, it's "just silly" if you will. Indeed the dollar symbol is often used in say political cartoons, financial cartoons, very much as a symbol of the US broadly.

If (for some reason) you wanted to use one symbol, you'd probably use the planet's main international currency, the euro, which is used by about twice? as many people as the USD, and of course in a dozen+ languages. (Of course, the Chinese Yuan is used by far more people than the Euro, and if I'm not mistaken there are now more net-users in China than anywhere else.)

(Oh - it turns out the the number of net users in China is double the US population ... again, another point suggesting it's "a bit silly" to use the dollar symbol.)

Moving on to a more positive note, what symbol should you use:

It seems quite common to use a melange of various major currency symbols:

Or, use "notes and coins" style icons ...

Or, use "bullion bars" style icons ...

There's three great choices, I think those are the main three choices open to you in developing an icon.

I'm from a country that is not using dollars as a currency. Creating an app depicting money using $$$ symbols would be silly. I mean if you are 10 years old, making an app for friends, then go for it. But if you are a professional and don't want other people laughing at it simply forget about it.

Depicting money as green bills or gold coins would be OK, even if we don't use green bills or gold coins.

Aside from the localisation issues, ¤, $, £ etc. are symbols of currency, not money. Since the stated goal is to create an icon depicting an invoice, how about simply using a basic calculation, for example:

^{download bmml source – Wireframes created with Balsamiq Mockups}

or simply

^{download bmml source}

Quite frankly if it costs 4 american dollars it should say USD

For canadian dollars CAD

And for new israeli shekels ILS

that way everyone knows the price in their currency,you can add a selection dropdown and or automatically detect the user's countries currency.

To be clear about this: the goal of showing this symbol of currency doesnt exacly mean money therefore this answer isnt very suited for the question.