Should BroadcastMicroblog include the broadcasting node's signature?

[sanity]

cc: @ravisvi

@nomel7 , @ravisvi and I were just looking through BroadcastMicroblog.java and notice that this includes a field that is the signature of the message using the private key of the node that's sending it.

I'm wondering why this is necessary, since I would imagine that messages should only require the signature of the pseudonym that created it, but not the physical Tahrir node.

Could you clarify this?