These have a bunch of features. You can engrave them like you would a tombstone for the urns you place on the shelf at the bottom of them.
You can also ‘Read Epitaph’ and it will cause your sim to cry and get a sad moodlet that will last for 4 hours unless they are Evil, and in that case will get a happy buff instead. If that wasn’t enough sadness for you, you can enable the emotional aura on these to give any sim in it’s vicinity a sad moodlet too.
The great thing about the Wall Epitaphs is that if the lot is set to a museum, other sims will come to the venue and automatically ‘Read Epitaph’ which will eventually fill your lot with sad sims. It's a great way to create your own makeshift Graveyard Lot!