UK Mac keyboards haven't got a hash key (or #) on them, to the frustration of Mac-based Twitter fans keen to create brilliant hashtags. So how can you type a hash on a Mac keyboard? And what about a euro symbol?
It's easy: Hash/# = Alt + 3.
(It has to be the 3 above the letter keys, however. The special numberpad on the right of the keyboard can't be used with modifier keys.)
Similarly, if you're annoyed that you can't find a euro symbol anywhere on your UK Mac keyboard, just use this shortcut:
Euro/€ = Alt + 2.
The Alt key is how you type lots of special characters on a Mac, including the Spanish inverted exclamation mark (¡ = Alt + 1) and infinity sign (∞ = Alt + 5). Consider these the second wave of special characters after those achieved with the Shift key.
Still more obscure special characters can be obtained on a UK Mac keyboard by using Alt and Shift. Probably the most useful of these are the Trademark symbol (™ = Alt + Shift + 2) and the symbol for degrees (° = Alt + Shift + 8).
For the really obscure, weird or just rarely used stuff, such as difficult mathematical symbols, specialist punctuation marks, Greek letters, Braille and some decorated numbers - or if you just can't work out an easy shortcut to type a special character - you can always use the special characters menu built into the Mac OS X operating system.
Press the Cmd (or Apple), Alt and T keys at the same time to bring up the characters menu. Double-click any character, and it'll be 'typed' into whatever document you've got open.
With all these special characters, however, bear in mind that some applications may not support every character. And some won't support the character pallet full stop. Experiment, and most of the time you'll be able to find what you're looking for.