A sigil beats a scar, a scar beats a staff, a staff beats a steed, a steed beats a sheaf, a sheaf beats a sigil.
Each coin has a value: sheaf is 5, steed 6, staff 7, scar 8, sigil 9.
Each coin can smile or shun, depending which side faces up. Smiles count as two of their kind, shuns instead knock out the lowest value coin from an opponent. Usually only one coin smiles or shuns per hand, but some gamblers insist playing with one of each. Playing where every coin can shun or smile is playing in the manner of gnolls, for whom the true test of skill in this game is being able to track the math, rather than how often you win.
A full purse is eight coins, a hand is five coins, a play is four coins. When you pull your coins you can pay a token of one of your highest value coins in order to take a look at your hand. Otherwise you must bet blind but you get to drop the lowest coin in your hand from play. After bets you reveal your hand and go to town.
Shuns take effect first. Coins triumph over each other as listed above. Once everyone's finished with their triumphs if there are still people in play (sometimes there aren't) then it goes to high coin, and then remaining multiples of high coin in order to determine the victorious Sceptre. Once that has been determined their opponent has one last chance for a Steal play, where they can try to make a pauper play (3 coins) from their fallen coins whose total is greater than the Sceptre's hand (or, in casual play, their highest remaining coin); the catch is that this play must contain one coin that the Sceptre's highest coin normally triumphs, e.g. You can only defeat a sigil if your play contains at least one scar and either staffs or steeds.
There are two other unofficial rules to mind.
One is the Stranger, a coin that nobody else at the table has, usually some foreign currency. If your hand has a stranger in it when you look at your hand then you do not have to discard your highest coin, you can instead drop the stranger. If you bet blind a stranger has no value but cannot be triumphed and can be used to break ties.
The other is the Slug, a token given out in lieu of normal pay, an IOU marker for soldiers. Slugs always count as two sheafs and cannot triumph or be triumphed.
If you're playing D&D 5e and you have proficiency with a gaming set that means you know how to play this game. Orcs bet brashly, halflings are little rules lawyers, dwarves try to yell everyone down and scare them off, tieflings are almost uniformly bad at this since if their genetic ancestors had much luck that didn't come from the devil then they wouldn't look like they do.
The entire story of how much action a soldier has seen, where, and under what circumstances can be told in a handful of coins. Any PC or NPC can get in at this if they have any pocket change. Like so many games that soldiers love in all realities the point of the game is not even to win but to eat up time and distract from looming concerns. Therefore circular rules arguments and bitching about obvious exploits are key parts of the process.
You will see soldiers wearing necklaces made with the coins they carry from fallen friends. They have a familiarity with currency that most treasurers would envy and can appraise and mentally convert most non-magical lucre easily enough. There are soldiers with leather wallets of strange coins they have found, like a binder of pokemon cards. Favored or lucky coins are left on the eyes of the lives they never wanted to take. You will see in the chapel a row of knights in solemn regalia and an elderly one-armed captain...he rises after the service and donates a small pouch, spilling an oft-mended pouch into the poor box. It is a small donation. It is an enormous gift.
This is a quick and dirty way of distinguishing your Fighters from each other and building in your backstory. The medic from Brescheau who only keeps sheaves and paints on the other suits. The Delt warrior prince who has had several platinum pieces smelted down and recast into a bespoke playing set. The young cadet whose purse is fat with his enlistment pay. The wounded pikeman lost in the Strangle who plays a game against a velvet voiced stranger in too-early forest twilight, a game where his opponent holds only a single smiling staff.
Again, many times you never make it past the triumph phase, players taking it in turn to risk their coins to knock others' coins out of contention. Again, the point is not to win. In that way it's like warfare. No, the point is to spend time with your friends and comrades before it's too late. Maybe get to know a new companion. Or perhaps have a conversation that only those thoroughly versed can comprehend, such as in enemy captivity. Pass a message by means of a distant traded copper.
Pickpockets know to steer clear of any person who jingles. That's not the sound of a dinner bell, but of a rattlesnake's warning of a weapon ready to cut its enemy down.