If you were able to leave a calling card/death card on you most hated enemy/faction...

What would it be?

There have been several discussions on this topic. In Oblivion as well. There I left a Daedra heart on my assassinated targets. In Skyrim, the human heart became a favored calling card.

My, I never thought about this. I'll have to think about that.

For no particular reason, a Jazbay Graqe.

If I did this, I would use a Crimson Nirnroot...

potatoes. lots of potatoes.

Talos amulets.

When I do use a calling card it's more for the homes I burglarize. I tend to leave one gold coin on the master bedrooms bed and then a child's doll right next to it.
Just how I duz it.

I had an assassin once who left a sprig of Nightshade on each kill.

I leave deathbells on my targets

I'm sure the last time I answered I said I left their decapitated head next to them an only their head.

Nothing, because leaving any investigators a neat little tally of your crimes would be a rather.. unthinking thing to do.

"Now we have finally caught you, murderer of two score and three!"

'That's rather a precise count.'

"Yeah, well, all we had to do was count black roses."

You're assuming they catch you!

Even if they don't catch you, it wouldn't do for a professional assassin to leave neat little clues for any investigator to find about his whereabouts, victims, methodology and any number of other things a sleuth would infer from combining all the information of all the crime scenes.

For an assassin, I prefer to be completely unseen going in and out and doing the deed with a bound dagger, or as I call it: "What dagger, officer? I don't carry one. Never have, ask anyone."

For that reason I really don't like the comments about the Solitude assassination you get from guards. "Heard you were seen in Solitude." 'No I wasn't. I made sure.'

someone else's calling cards or clues so they can't come after me...

"It wasn't me sir, you can see the assassin left their mark! A crimson nirnroot placed on the heart, it had to be the Red Prowler!"

How devious. I like it.

This.

There usually isn't a body left when I finish my targets.