California rules of professional responsibility warn attorneys against calling themselves a “certified” specialist unless they hold such a title from the California Board of Legal Specialization. And LinkedIn has a helpful section of its “experience” section called “specialities.”
Are you at risk for violating the California rules of professional responsibility if you put any text in that field? Probably not. However, if you put “real estate” or “estate planning” you probably increase the risk of putting yourself forth as an expert in those legal specialities and might want to only do so if you are in fact certified by the state. If you want to be completely safe, just skip that section of your LinkedIn profile.