If you live in the UK, you may notice that your Apple Mac doesn’t have a # symbol on the keyboard. In the US they # sign is on the 3 key, but instead we have the £ sign instead.
To type #, simply press ALT+3 or OPTION+3
An interesting fact. The # sign is called ‘hash’ in the UK but often called ‘pound sign’ in the US, which is the same name we give to our currency (£). You can therefore easily remember the shortcut as an ‘Alternative way to say pound/£’ (ALT+3)