I have put the Arentino kid's plate one of my empty wall shelves (in the back room of the ground floor). It looks nice sitting there, but it seems like it could use some sprucing up. I was thinking about putting a sprig of nightshade on either side of the plate, or perhaps have it flanked by skulls. But I was trying to think of some DB related items, preferably unique items, that could be put on the shelf with it. Any ideas? Note: I have destroyed the DB, so items you obtain during that questline are not available.

For DB related items, especially if you have destroyed them, an idea could be the Dark Sacrament book. Although not unique, it kinda fits your idea.

Put the gloves you looted off Astrid's corpse next to it, since they're the ultimate assassin tool.

Ooo, nice idea

A dagger would be a nice touch. Since you destroyed the DB, I suggest using the heirloom as a plate and displaying all of the assassins' notes on it. Perhaps with some of their gems, or whatever you've looted from their corpses.

Seeing as you destroyed the DB, not really sure on other items to display. One item may work, Nazir 's Hood is the only "Red" Redguard hood in the game.

If one was to complete the DB quest line I would suggest the following.

Vittoria's Wedding Band and Wedding Wreath are two items I have on display with Arentino Heirloom and Astrid's Dagger.
I also have the Emperior's Robes and Vittoria's Wedding Dress on dispaly also.

"What is the music of life?"
"Silence, my brother."

Thanks to everyone for their suggestions.

Here is what I ended up doing. I put it on the right hand wall shelf in the back room. It is standing upright leaning against the wall. On either side I have a skull facing away from the plate, one to the right, one to the left. (Gettting those skulls positioned was HARD!) I then put two sprigs of nightshade in front of it. It looks very nice.

I didn't use any of the clothing suggestions since I wanted to display those on mannequins. I have three DB related mannequins. One displays shrouded armor. Another displays shrouded robes. And the third displays Nazim's clothes. If I can get my pickpocket skill to 100 (it is at 98 now) I am going to go get a Penitus Oculatus outfit from one of those guys up in Dragon Bridge. Or I just might kill one and take it off his body.

I am having real problems tyring to display the Blade of Woe. I tried putting it in a display case in a HF house, but it would not behave. So I went to Vindrel Hall and tried puting it on weapon plaque, but it didn't like that either. And when I put it in a dagger case, it ended up moving around. So now it just sits in a cabinet. I'll have to work out something for that.

Maybe it just wants you to carry it around with you. So it can kill things.

On my assassin character (which hasn't been played since finishing dawnguard when it came out) has the plate on display in her home surrounded by deathbell flowers. She left a deathbell flower on the corpse of every target as a calling card. seemed fitting.