Your attorney's two responses capture exactly what I'm talking about.  On a resume, an honorable person would be precise and write "Lecturer, University of Chicago School of Law."  But when you're talking about what you're doing, you don't say "I'm a constitutional law lecturer."  No one does--just as Lars says.

A simple way to think about the distinction is whether or not the word you're using should be capitalized.  Obama's title was "Lecturer," but his job was as a "constitutional law professor." In the same vein, I have a Ph.D. in English, so if anyone actually knew this, they might choose to refer to me as "Doctor Deminva," although I certainly don't work as a doctor.

As your attorney's response indicates, it's not uncommon for an adjunct professor to include the word adjunct when talking about what he or she does -- precisely because it's just an adjective added to the common word, i.e., professor.  

Bottom line: If you or anyone else can find any campus in the US where students say things like "Hey, who's the lecturer for that course?" or "Hi, Lecturer Jackson!", then you may have a case.  

Note, too, that as a state legislator, Senator Obama most likely had the title of Lecturer because he wasn't full-time faculty or because his legislative duties precluded his involvement in the sorts of things that tenure-track faculty do besides classroom teaching.  It wasn't that he couldn't get hired as an Assistant or Associate Professor at Chicago.