Get the stock certificate from your financial planner or bank, along with a stock power document. You will need both of these things to complete the remaining steps.
Prepare the first envelope to be mailed. It will contain the unendorsed stock certificate (this is important--if it is endorsed anyone can cash it) and a letter indicating the person to receive the stock certificate along with your complete contact information.
Assemble Envelope #2 to include a signed, signature-guaranteed stock power. Address both envelopes completely with your information and the recipient's information.
Take them both to your local post office and asked them to be mailed Registered. It would be wise to have delivery confirmation and a signature for the recipient only added as well. If you are sending a large amount, consider adding insurance.
Advise the recipient of the date and method of which you mailed both envelopes. Ask them to alert you once they arrive safely.