I just saw weird Orokin scripture on a black background, didn't get a screenshot though...

[DontRunWScissors]

Was this a teaser for a previous quest?

[xXDeadsinxX]

If you’re talking about the one during the loading screen then it’s old, it was a teaser for the Second Dream quest. 

[(PSN)s3d_sas]

I am your reckoning!!......... *wink* *wink*

[DontRunWScissors]

It showed up after I finished an invasion mission on Sedna, and it didn't cover my whole screen, it was there while I was in my Orbiter

[Sunai_Moonswing]

It's your "warframe boot up" something from Margulis. From the old war, before the Jade light.