There are probably as many mourning traditions as grains of sand on a beach, when one considers the whole of Arvum.
There is, however, only one custom that is shared among all those in the Compact. When a loved one dies, some of their belongings will be portioned out to craft peace knots that can be used to bind weapons to show respect for the dead.
((OOC: peace knots are not yet coded, but they are assumed for all "official' places and events within Arx - and enforced there. Until they have a recipe and function you are free to just pose them))