Unless you're feeling extremely pretentious, exactly the same way you always have. In some contexts it may make sense to append the abbreviation for the specific degree, but outside of a formal...
Unlike a doctor or lawyer, holders of a master's degree (in the U.S.) do not typically place any sort of title in their daily name. That is, there is no masters equivalent to Dr. or Esq.
It depends on the degree and its classification. For example, if you have two degrees and both are a master's of arts, you indicate just M.A. In other words, John Smith M.A. If they are in different...
The bachelor's degree is generally not appended to the signature so presumeably you mean two graduate degrees. Keep in mind that even then appending the degree to your signature is usually done only...