I have PM'd
etotheipi asking him to kindly join in the discussion about how to best sign a paper wallet.
I neither endorse nor discourage signing like this. There's a lot of ways that this kind of signing could be abused, such as Ken simply knowing someone who has 1,500 BTC+ who would be willing to sign such a message for him (it doesn't really hurt the person who signs on his behalf).
Ideally, your message would be something like:
("Ken Slaugher and ActiveMining have full control over this address which, at the time of signing, has 1,500+ BTC.")
However, this is most effective if you know a particular address in advance. i.e. You are already aware of a specific address holding 1,500+ BTC, and you want Ken to prove he has control of it. Though it's still not fail-proof, if somehow Ken knows who owns that address and gets them to sign for it (but better than Ken simply needing to find anyone with 1,500 BTC and sign it).
With all that in mind, if you don't have a particular address in mind, the best you can do is:
Someone with at least 1,500 BTC was willing to sign the following message:
"Ken Slaugher and ActiveMining have full control over this address which, at the time of signing, has 1,500+ BTC."
The address associated with the signature can be looked up on something like Blockchain.info to verify the money held by it.
You can do this easily with Armory, even if it's not an Armory wallet. You can create a wallet on an offline Armory instance (such as in a live session), and import the private key to the wallet. Then you can go to "Tools"-->"Message Signing" from the main window and use that private key. I don't recommend doing this with versions of Armory older than 0.90-beta. The old message signing interface was garbage, but was updated in 0.90-beta, and you can now make signed message blocks. The signed message block could be copied to USB key or exported somehow, then the offline/live session destroyed.
As said above though, given the circumstances, I'm not sure how useful this will be.