Vaguely Spanish-influenced... why not address non-noble folks as Sen~or, Sen~ora; or bend it a bit Italian-ward, Signor/a; or Portuguese-ward, Senhor/a ? Maybe swap the feminine -a suffix with -e to invent a nongendered professional form similar to Mx. The feminine form already covers both Ms. and Mrs.
Or if you want an abbreviated form that's not "Ser", perhaps "Sen" or "Sn." --if you don't have Senators to be confused with average folks?