That's exactly what I thought when I saw them. Especially since in the RoC cinematic, he holds up the crown like that. (well... not exactly... but y'know)
This was actually a 3D model or something made by someone for the blizz art contest or something like that... I think.
Those rose petals are indeed the ones from RoC. They are known as "Arthas' Tears" in WoW, which were thrown down upon Arthas cheerfully as he walked down across the path to King Terenas' Throneroom. In WoW, if you look closely and zoom in, you can still see the pedals on the ground over the path he walked in Undercity.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.