Being that you're a web designer it's well worth being aware there is no hash key on Macs, which is incredibly useful when coding CSS.
Shortcut: Option+3 (Alt+3)
I realise you could search but hey, a heads up is always a bonus!
mate I am lost, is your keyboard different to mine, because my Mac has the # symbol right above the number 3, all I do is hit: Shift + 3
unless you call something else hash, but seeing as the # is used in css, i assume you mean that.