No, “ex.” is listed as an abbreviation in for example the American Heritage Dictionary (Second College Edition, 1982), though “example” is only the second of seven meanings listed for it: 1. examination 2. example 3. except; excepted; exception 4. exchange 5. executive 6. express 7. extra “e.g.” is listed as Latin for ”exempli gratia (for example)”, so a slightly different form.