It's a thank-you note from the Lotus for the best Stomp of her life.
It says "D'AE'NG'IH'R" which translates to "DANGER" in Orokin Language.
So if Rhino "stomp'd" The Lotus she would be in danger... :D
Nope, not Danger. Danger is on his back. The thing on his shoulder is the same with Nekros', Evolution. At least I think so.
Oh yeah, your right.
that marking can be found on every warframe (in varying places), excalibur for example also has one on his shoulder
What do you think?