It is social proof IMHO. A social proof of one, but a social proof nonetheless - social proof coming from a fellow HN user might add some authority to the mix:

"social proof: People are more willing to take a recommended action if they see evidence that many others, especially similar others, are taking it."

"authority: People are more willing to follow the directions or recommendations of a communicator to whom they attribute relevant authority or expertise" (summary of Influence: http://www.sellingandpersuasiontechniques.com/influence-summ...)

I've read Influence - great book. What do you think the difference is?