It's been a while since I've done this, but I think you can just mail the certificate with ordinary mail. Instead of signing the certificate, which makes it negotiable, ask your broker for a "stock power" form, sign it, and send it to the broker under separate cover.
(1) Do you really need a stock power form sent under separate cover? I thought these days certificates had wording on the back such that they could be filled out in a manner similar to "for deposit only to..." on a check, so that the certificate would NOT be negotiable.
(2) Even if the certificate is non-negotiable, that doesn't eliminate the pain in the neck and red tape you'll have to go through if the thing gets lost anyways. So still consider a higher, more secure class of service than 1st class mail.
Here's what the Fidelity website says about sending a stock certificate to them. Similar guidelines probably hold for other brokerages.
You can deposit stock certificates directly into your Fidelity Account using the following guidelines:
All account owners must sign their names exactly as it appears on the certificate(s).
Note: If registrations do not match exactly, including the spelling of names, complete a Certificate Release Request Form (PDF) or send Fidelity a signature-guaranteed letter of instruction signed by all owners of the account.
Write your Fidelity Account number in the top right corner of the certificate.
Write National Financial Services LLC in the blank space between appoint and attorney on the back of the certificate.
Certificates may be sent by certified or registered mail; we recommend insuring them for 2% of their value.
You'll find similar recommendations when mailing certificates back to the issuing company. Lockheed's site gives an underlying rationale for the insurance - one insures for the amount at risk, and companies typically charge around 2% to replace a lost certificate. (Lockheed suggests 3%, so that's probably what Lockheed charges.)
BeanSmart website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.