What does "Leave a calling card on your victims" do?

The new update today removed all item set bonuses and made them slightly different.

The wiki pages for each set's effect reads:

Leave a calling card on your victims

What exactly is this calling card. Is it a particle effect? Does it change gameplay whatsoever?

The calling card is a set-themed tombstone that is left at the spot where you killed your victim. Currently calling cards are only left by sets that previously had positive effects (removed in the July 10, 2013 patch).

Here's an example of the sniper's croc-o-style set calling card from the steam community:

And pyro, and scout and soldier and ...