Resolution of the "GPG signature verification error" prompt

When Ubuntu executes apt-Get update, the error of GPG signature verification is reported.

W: GPG signature verification error: http://ppa.launchpad.net intrepid release:
The following signature cannot be verified because there is no public key: no_pubkey 19c98318f87fe1bd

Solution from http://forum.ubuntu.org.cn/viewtopic.php? F = 77 & t = 182819 found:
Download key:
GPG -- keyserver subkeys.pgp.net -- Recv ********
Import key:
GPG -- export -- armor ******** | sudo apt-key add-
Note: * indicates the last eight digits of the key.