To me that's something that would be better indicated by (or on) the line joining the couple.
Maybe I am being very stupid, but what is the advantage, please? Ancestry allows me to make prodigious notes on any relationship. My cousin was very promiscuous, one of her one-day partners and the father of her 5th child was "Unknown rugby player, Clifton College First XI". How that would translate into an emoji, I don't know.
Regards
Chas
Not stupid at all Chas

Like Colin I prefer to see as much basic information as possible on the tree view. Yes, it's easy to add just about anything you can imagine as notes*, so I can easily do it that way as well.
But to find those notes later I have to click on the individual and navigate to the relevant piece of information - at least one more click I think (to see the 'full profile'). I have a very old computer with a slow internet connection and after each click it takes some time to update. And then I go back to the tree which also takes time. So it's rather tedious.
When I draw a partial tree by hand I often write the marriage year on the connection along with any relevant notes, e.g. "unwed, 1 child", "no kids","div.1964". I was surprised that none of the three sites seem to do this.
You ask "what's the advantage?
1) When I look at my tree after a long gap it helps me recall some basic things without the frustrating clicking around.
2) Anybody viewing the tree (I have a public tree on each of those three sites) can see the same basic stuff at a glance without having to dig around.
*P.S. I found that that MyHeritage has a field for relationship type (married, widowed, divorced, annulled, separated, etc) when you add/edit a spouse. I'd missed that when I originally posted this topic.