One mark, one colour per branch
The reunion shirt that survives a decade is a crest and a year, printed small, in a different garment colour for each side of the family. It solves the design and the seating chart at once.

Nine shirts, four colours, one mark. An oak-leaf shield with a year under it, printed small on the chest.
That's a family reunion solved — and it does two jobs at once, only one of which is design.
Why one mark instead of a big graphic?
Because the shirt has to survive being found in a drawer in eleven years.
A reunion shirt has a long second life. It gets worn to mow the lawn, it gets inherited by a teenager, it turns up in photographs at the next reunion. Anything that was funny in the moment — a slogan, a cartoon, a list of everyone's nicknames — ages badly and gets thrown out.
A crest and a year doesn't date, because it was never trying to be current. The no-fail version across every family that does this well is the same: a mark, the surname or the year, and nothing else. It works for eight people and for two hundred.
What year should be on it?
Not this one. The year the family started.
The shirt above says 1927 — the year the line began, or arrived, or bought the farm, or got off the boat. That's a considerably better number than the date of this weekend's barbecue, because it's the same on every shirt ever made and it's the thing the reunion is actually about.
If you want this year too, it goes small, on the sleeve or the back. The founding year is the headline.
What's the trick with the colours?
Each branch of the family gets a different garment colour, same print.
That's the part that earns its keep. Everyone in the black shirts descends from one grandparent; everyone in the rust ones from another. You can see the shape of the family from across the garden — who belongs to whom, who married in, which branch turned up in force.
It also solves the objection people have to matching shirts. Nobody feels like they're in a uniform when the order spans several colourways, and the kids can pick. It's a set rather than a uniform, which is the same distinction that makes group shirts wearable anywhere.
Which colours?
Heritage tones, and this is one place where the received advice is right for a real reason.
Deep green, navy, burgundy, rust, brown, charcoal, dust blue. What to avoid is bright primaries — not for taste reasons, but because they photograph badly and they age badly, and this particular garment's whole purpose is to be in photographs that get looked at decades later. A neon shirt in a 2036 photo looks like a mistake; a brown one looks like it was always that colour.
The washed cotton here is already in that range, which helps.
What should the crest be?
Something from the family's actual world, drawn simply.
Not a purchased heraldic coat of arms for your surname — those are sold by the thousand and almost never connect to anyone's actual ancestors. What works is an object: the tree in the old garden, the boat, the shape of the county, the tool from the family trade, the flower that grows on the farm.
Oak leaves in the picture above are a good default because they're a shape everyone reads as lineage. Yours will be better if it's a thing somebody in the family can point at.
How big should it print?
Small. Chest-pocket scale, not full width.
This is a shirt people who don't like graphic tees have to wear, and small is what makes it acceptable to everyone. It also puts the mark at the height it appears in a group photo, and keeps the design out of the way of the fact that four generations are standing in a garden.
Full-size chest prints suit shirts you chose. Group shirts you were handed do better modest.
Do we have to order them all at once?
No — and that's the change worth knowing if the last reunion was a while ago.
There's no minimum here, so the count doesn't have to be right in advance. Somebody who didn't reply can get one later; the cousin who arrives with a new partner can order theirs the week after; the design stays available for the next reunion. Guessing quantities was always the worst part of organising this, and it's gone.
How do I get one made?
Describe the crest at JustOG — the object, the year, and how many colourways you want. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
The colour tells you which grandmother. The year tells you why everyone came.