I know you're not supposed to 'use the lord's name in vain' but?

It's only within the Hebrew Scriptures and tradition that that practice is observed. To say a name or to name something is to have control over it - so it is in Genesis that man "names" the animals. But man (in the Hebrew tradition) cannot control or own his creator. So you'll see G-d or YHWH and similar abbreviations. Additionally, in Hebrew whenever the word G-d appears in written form the word Lord or Adonai is pronounced instead.