By default, couples are shown with an = symbol between them on charts:
Setting the couple’s status to "Never Married" (in the People panel) changes the symbol to x:
"Cohabiting" keeps the = symbol (which is more polite) but updates the chart key to note that it is also used for non-married couples.
Adding a divorce fact to the couple (Facts > Add Couple Fact > Divorce) shows the = symbol with a bar through it:
An annulment fact produces the same symbol. Removing the divorce or annulment fact removes the bar.