Security Warning Light Flashing?

I've got a 2010 4-door hatchback and yesterday installed replaced the factory radio for one from crutchfield. I detached the negative battery cable to do the work. After all is done and everything is working, I noticed the red security warning light is flashing constantly.

The owner's manual says that when the power button is turned off, this light will flash. That's about all it says. It could mean continuously until the prius is turned on or it could mean it will flash to let you know it's ok and than stop.

Neither my wife or myself remember whether this is normal behavior. Having just done the receiver install it concerns me. I called my dealer on Saturday, and the guy I talked to remembered there was a light that did flash continually, but he couldn't name it, and wasn't going to research it for me.

Help me gain a sense of security (pun intended) and confirm this is normal behavior, if you can. Boy you'd think we'd remember this ourselves since we bought the car new.

 

Yes, that helps. Particularly the "always been that way" part. Thank you.