I ran a game of 13th Age last night on Roll20 with for the first time with a player playing a Rogue. It was then that we discovered that tracking the Rogue's Momentum was going to be tricky. When the Rogue hits an opponent, they gain Momentum, and when they miss an opponent they lose it. So today I created a poker chip to keep track of Momentum. Just create a deck of cards called Momentum, and use this graphic as the front and the back of the card. Be sure to create two cards and make the deck infinite. Now the player can just grab chips of the deck when he gains momentum, and chunk them out of his hand when he loses momentum. Hope this can help others.