The euro sign € is the currency symbol for the euro. Here is how to type it.
Windows
Hold Alt and type 0128 on the numeric keypad, or press AltGr + E on a European layout.
Mac
Press Option + Shift + 2 on a US layout.
Phones
Switch to the numbers and symbols keyboard; the € is usually with the other currency signs.
Facts to verify: Alt+0128, AltGr+E and Option+Shift+2 on current OS versions and keyboard layouts.