Oh cool, I looked at this earlier and thought of 7 Swords & 3 Pentacles for signing documents, with Justice then they would be legal ones of some sort... , but thought maybe I was in left field... thanks Zach & Joermit for adding your thoughts to confirm my own eureka moment.
Seven Swords is often legal matters, using your head, discernment, expression of thought, deliberation, negotiations to arrive at some successful resolution and the first card that popped into my mine was the old man with a feathered quill laboring over a parchment in Druidcraft's 7 Swords.
I also thought of 3 Pentacles too, because it's usually is making a mark of some kind with witnesses to document it.
8 Pentacles would be something more repetitious, like signing autographs or maybe writing checks to pay bills, sending out Christmas cards, etc.