How can I get "WHITE SMILING FACE (U+263A)" with the keyboard?
In Windows you can:
Left Alt + 1 : ☺
But the number must be from the Numeric Keypad
You can also:
Left Alt + 2 : ☻
In Ubuntu (and variants thereof, like LinuxMint) you can enter Unicode values by pressing Ctrl+Shift+u followed by the Unicode value and Enter, for example:
Ctrl+Shift+u 263a yields:
You might be able to couple this with AutoHotkey for easier input, or possible input in Windows.