Do you really expect somebody owning 6700$ in BTC would care for 1.7$ prize?!
I have a paper wallet with less than 1BTC on it, but it's not worth the hassle for the 10 cents you'd give.
and the 10 cents may cause you lose your 6700$. lolz... becareful folks...
Signing a message doesn't make people lose money, unless maybe it's done from an extremely buggy client
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
But the meaningful way to keep bigger amount of Bitcoin is in cold storage or paper wallets. And that means extra hassle to sign a message. And the reward is way to small for any kind of hassle.