This has been bugging me the last few days, so I'll say it.
THE PSP HAS NOT BEEN CRACKED WIDE OPEN.
NO WE CANNOT SIGN HOMEBREW YET.
The so called "signed" homebrew and HENs that have been released so far are all using a trick that requires the encryption keys, hence the name of the tool, PSPencrypter and NOT PSPsign. The tool encrypts the homebrew, and wraps it with a demo games signed "box", so to speak. This tricks the system into thinking it is signed. People on #pspcommunity have been calling these wrapped homebrew, considering that's exactly what they are. Some have also been using "signed", with the quotes, however I find this will confuse people when signing is possible in the future.
Don't get me wrong though, this is still very useful, but it's not done, and there is still a lot to be done before signing is possible. I have not tested the new 6.37, but most likely this trick has been fixed, if not, it will probably be fixed in the next one, so don't expect these wrapped homebrew to work forever.