Asymmetric Cryptography usually uses a public and private key. Think of this something like one password to encrypt something, one password to decrypt it. You release your public key so that other people can send you messages only you can decrypt, or so that they can verify a given message is from you and only you.

The problem is, while this technology has been available for decades, it still isn't widely used. A good example is the Hacking Team dumps recently. A group that really should have been encrypted their emails wasn't, except for a handful of times.

This comic is stating the the character has had a public key available online for years, but has never received any mail using it. He posits that if he made his private key public too, he may get more usage of his keys. The mouseover text is a joke about crowd-sourcing.