Screenshot says it all...

Think it means you've been hit by an engineered weapon. There was a guide to them on the beta forums somewhere.
Maybe it's indicating that your shields are being affected by a shield loach.
I'm aware of symbols that appear when you're hit by these things. However, this thing persisted for several minutes.
One of the devs did say that they would be explained in an update to the manual - presumably the one avaiable through the launcher - after release.
I'm unsure if that has been updated yet.
Maybe a corrosive weapon? I can imagine a longer time until the effect wears off...
It's internal damage, as far as I can see. I was getting it while overheating during fuel scooping.
The answer is in this Training Video at 5:05.
https://youtu.be/vXiX0CYDpxM?t=305
http://i289.photobucket.com/albums/...gerous/EngExperimentalEffects_zpsagowubth.jpg