Using the Cent Sign
The cent sign is a lowercase c with a vertical or slanted stroke and it marks one hundredth of a dollar. It belongs to the same Latin-1 block as £ and ¥, so it has an Alt code, a Mac shortcut and a place on every phone keyboard, and it renders on any device made in the last thirty years. Despite that, it has almost vanished from everyday typing because cash registers, spreadsheets and online shops express everything in decimal dollars.
After the number, and never with a dollar sign
Unlike nearly every other currency sign, ¢ follows the figure: 25¢, 99¢, with no space. The classic error is combining it with a decimal dollar amount, as in .99¢ or $0.99¢. The first literally means less than one cent; the second mixes two ways of writing the same thing. Choose one: $0.99 or 99¢. Signs in shop windows get this wrong so often that it has become a running joke among editors, so it is worth pausing before you print.
Which countries use it
The United States, Canada, Australia and New Zealand all read ¢ naturally, and the sign appears on price stickers, coupons and fuel pumps. Australians and New Zealanders often type a plain c instead, 50c, and that is accepted in print there. The euro has a cent as well, but eurozone usage writes it as a decimal, €0.50, or spells the word; the ¢ sign is not part of European price typography. Other currencies with hundredths, such as the pound with its pence or the yen with no sub-unit in circulation, never use it.
Lookalikes worth checking
The Ghanaian cedi sign ₵ is almost indistinguishable in many fonts, and the Costa Rican colón sign ₡ adds a second stroke. Both are real currencies, so the wrong character on an invoice changes the meaning rather than just the look. East Asian keyboards produce the fullwidth ￠, which is fine in a message but will not match a search for the ordinary ¢. In the other direction, the generic currency sign ¤ is what some older systems print when they cannot identify the currency at all, and people sometimes assume it is a broken cent.
Typing it
Windows takes Alt + 0162 on the numeric keypad; a Mac gives it with Option + 4; and iPhone and Android keyboards keep it under a long press on the dollar key beside the euro sign and pound sign. In HTML the named entity ¢ works in every browser, and in LaTeX the textcomp package provides \textcent.
In bios the sign shows up in a few playful ways: "my 2¢" for opinions, "0¢" jokes about free content, and as a decoration on thrift and vintage accounts. It sits well beside plain characters from the aesthetic symbols list and survives username filters that reject anything outside Latin-1.